Sir: Johann Hari (17 March) supports the proposal that we should all be entered on a national DNA database. The underlying suggestion is that none but the guilty have anything to fear. Nothing could be farther from the truth.
As each of us goes about our daily business, we deposit DNA all around us; the Forensic Science Service (FSS) on its website boasts that the latest techniques can detect "the amount of DNA left on a cup by drinking from it or on a pen by writing with it". Every crime scene is likely to contain large amounts of DNA deposited by persons unconnected to the crime – forensic-science journals have published papers confirming that it is possible for DNA to be passively transferred from one scene to another. This means that the presence of an individual's DNA at a location or on an object does not even prove that person has been in contact with that scene or object. When everyone's DNA is in the system, none of us can rest easy that we will not suddenly be accused of involvement in a crime of which we know nothing.
Once police are presented with a suspect they tend to focus on a search for incriminating evidence and ignore or even, in some shameful cases, conceal exculpatory evidence. If even a minute, invisible speck of material bearing your DNA has been found at the scene of a serious crime, the onus will be upon you to convince the police that you are innocent.
Surely we can rely on the CPS and the FSS to ensure that the technology used is as infallible as possible? Again, sadly this is not so. The technique called Low Copy Number (LCN) has been rejected for use as evidence by all but three countries, and by the FBI, because it is deemed so unreliable. Despite this, and a scathing condemnation of the technique by a High Court judge in Belfast, the FSS continues to use this technique. Combine the use of LCN with a universal DNA database and the question becomes not "Will there be miscarriages of justice?" but "How soon will the first one occur and how many will it take for the system to be reformed?"
The great lie about British asylum
Sir: In 1989 I was tasked with setting up and heading the first dedicated political asylum unit in the Home Office. Nineteen years later, the Independent Asylum Commission has added nothing to the debates that raged at that time (report, 27 March).
The international asylum system raises awkward questions. Why does a woman at risk of genital mutilation deserve sanctuary, but not one who is starving to death? Or a man at risk of torture, but not one dying from a preventable illness? Can we offer a home to all who live in societies that disrespect women, homosexuals and human rights? If not all, then how many?
The Commission neither asks nor answers these questions. Instead it argues for a status quo which is not working, and repeats the cliché of "Britain's proud record" of asylum. In so doing, it perpetuates the lie – of which asylum-seekers are the victims – that our borders are open to all those who face persecution. In reality, geography has ensured that Britain has never received mass refugee movements, and we continue to do all we can to prevent new arrivals.
A French politician said of asylum: "France cannot be the receptacle for all the miseries of the world." No British politician has had the courage to say the same. We need an honest debate about the limitations of the 1951 Refugee Convention, which treats migration as the only solution to persecution. The Commission does not invite that debate.
N C Sanderson
Sir: Peers concerned over the asylum case of Mehdi Kazemi ("Asylum: the peers revolt", 28 March) are absolutely right to be extremely alarmed at the frightening number of executions in Iran.
As we will show in graphic detail in our forthcoming annual report on the use of the death penalty worldwide, Iran is now second behind only China in its widespread use of capital punishment.
Given that torture in detention is common in Iran, and that those executed have included child offenders (aged under 18 at the time of the alleged offence), and people accused of the "crime" of adultery, the situation is bleak indeed.
Members of the House of Lords are clearly up to date on the appalling reality of human-rights abuse in present-day Iran – is the Home Office?
Campaigns Director, Amnesty International UK, London EC2
Sir: The Independent Commission on Asylum was chaired by a former judge. Its distinguished members spent months travelling the country, talking not only to asylum-seekers and those who care for them, but to the civil servants responsible for their deportation and to members of the public who feel the system is too lenient. Yet the minister responsible for Asylum and Immigration, Liam Byrne, has dismissed their findings, saying that the system is completely fair. Does he really believe these eminent people gave up their time to produce a work of fiction? If compassion, fairness and respect for the truth are the values we want to identify as "British", this detailed, evidence-based report should not be dismissed by the Home Office but used instead to reform the way we treat vulnerable asylum seekers.
Don't panic about Parkinson's disease
Sir: I would like to correct the suggestion made in your article on Parkinson's disease (24 March), that "three quarters of people over 70 will have Parkinson's to some degree".
National Institute for Clinical Excellence guidelines for PD state that 100 to 180 per 100,000 of the population are affected by PD and, although incidence increases with age, this would still be only two per 100 over 80 years. About 10,000 new cases will be diagnosed annually.
To suggest that 75 per cent of the population over 70 will develop PD is misleading and alarming for those reaching that age (my mother, in her early 80s, was certainly worried). As a physiotherapist specialising in treating this condition, I would encourage anyone affected to seek support and therapy for help in alleviating the symptoms.
Happy 75th birthday for polyethene
Sir: Rob Sharp claimed the world would not be celebrating the 75th anniversary of the discovery of poly(ethene) (26 March). In fact, we organised, on behalf of the Macro Group, Royal Society of Chemistry and the Polymer Physics Group, Institute of Physics, a one-day meeting on 27 March at the Science Museum in London to mark this event and to reflect on past successes and explore future challenges. The Plastics Exhibition at the Science Museum houses the original equipment used in the discovery. Present were a number of scientists and guests including (to name but two) Ron Gibson, son of one of the original inventors, and Professor Walter Kaminski, a pioneer of a route to the controlled production of a range of poly(ethene) materials which are more likely to be found in the space shuttle than your local supermarket. If polyethene was dead and buried as Rob Sharp proposes, there would be no safe water (poly[ethene] pipes), no safe electrical cabling (poly[ethene] insulation), no replacement hip joints... the list goes on.
Professor Geoffrey Mitchell, University of Reading; Dr Fred Davis, University of Reading; Professor Alun Vaughan, University of Southampton
Money alone won't save the rainforest
Sir: Small countries often lead where giants lumber behind, and Guyana's offer of its rainforests to global stewardship is a good example (report, 27 March). This is vital, for we now realise that industrial-strength deforestation in the tropics is a deadly factor in global warming, and, at last, there may be serious money available to prevent it.
But after 20 years working on tropical conservation, I've seen that money alone can't buy it. The forces that destroy forests have huge momentum, and can obliterate ecosystems even when governments and financiers wish otherwise.
To oppose this danger, millions of people are needed, their eyes alert to the tell-tale signs of forest invasions, their mobile phones reporting fires and roads made by loggers, their votes and actions demanding enforcement and compliance. With everyone a citizen scientist, illegal logging, farming and ranching, which thrive in darkness and corruption, can be made to shrivel in the light.
Everyone can help by observing, investigating, and reporting. This is the great challenge of our times. Your biosphere needs you!
Dr Julian Caldecott
Top architects: your country needs you
Sir: You rightly support the criticisms of Lord Rogers regarding the poor quality of domestic housing development (leading article, 29 March). Unfortunately, the pressure to build ever more quickly and (relatively) cheaply will continue, from government and developers.
The young architects you expect to raise standards will not be able to withstand this pressure while their jobs are at stake. The people who need to do something about this problem are the famous and justly wealthy architects. Neither Lord Rogers nor Lord Foster can be in need of money, so why can they not give a little time to proposals for domestic housing estates?
More than ever we need someone with their level of influence to show government and developers that solutions can be found that are cost-effective, ecologically sound, environmentally sensitive, functional and long-lasting.
Sir: I read with great interest your report and leading article on Richard Rogers and his views about urban regeneration. Surely we all agree with his views on "shoddy toy-town houses and Dan Dare glass towers", but while I know of nothing in his considerable output that resembles the former, I do associate him with the latter, with his designs for such towers in, among other places, the World Trade Center in New York and the "Cheesegrater" for Leadenhall Street in London. I'm extremely puzzled as to what distinguishes these from the "Dan Dare" towers he says he so dislikes.
How to deal with disruptive pupils
Sir: Given that prevention is better, and cheaper, than cure, Jane Downes's letter (27 March) on smaller classes makes obvious sense. Deborah Orr recently described resentment that misbehaving pupils ended up in small groups at pupil-referral units – they were "rewarded" by getting more attention.
Having worked as a teacher with some "misfit" pupils (years 10-11), I can offer a couple of observations. First, close attention from a sympathetic teacher means that some difficult pupils actually manage, at last, to apply themselves to and complete pieces of work, achieving something other than failure. Second, when disruptive pupils are removed from lessons, the remaining co-operative pupils work well, even when groups are merged into larger class sizes. A win-win situation.
Maggie's marital status
Sir: Surely Terence Blacker is wrong (28 March) to describe the previous two Conservative Prime Ministers as "one a divorcee, the other an adulterer"; Margaret Thatcher may indeed have married a divorced man, but she was not divorced herself.
A profitable post office
Sir: Christopher Lumb (letter, 29 March) suggests that Royal Mail could learn lessons from the French on how to run a profitable postal service. In fact Royal Mail was profitable for 23 consecutive years up to 1999/2000. The lion's share of that money was taken by the government as dividends, when it should have been invested in modernising equipment and methods. Perhaps the most important lesson we could have learned from other countries would have been to ignore the "liberalising" Postal Services Directives, 97/67/EC and 2002/39/EC, rather than rushing to implement them.
Dr D R Cooper
Sir: No, Mr Richardson-Howell (letter, 28 March), we shouldn't give our former prime minister the benefit of the doubt. He didn't give it to the Iraqis who said they didn't have WMD and who were backed by the UN investigators. The only explanation for his behaviour is precisely his unshakable equanimity, self-belief and self-justification, reinforced by his strong faith – that is to say, his refusal to take anything into account which wasn't inside his own delusional head or to admit he could be as wrong as the rest of us know him to be.
S R Hills
Scottish MPs' expenses
Sir: Could I quietly remind your readers that every detail of Members of the Scottish Parliaments' expenses are open to view on the web. There have been one or two deserved embarrassments but, so far, the sky over Scotland hasn't fallen in.
Sarko's missed chance
Sir: In all the coverage of the recent state visit by the President of France and his wife, nobody seems to have been particularly concerned that they did not travel here by train. The Channel Tunnel, with its now magnificent new British terminal at St Pancras, is one of the finest and most tangible symbols of successful Franco-British co-operation. What an important environmental message an arrival by rail could have sent out – and, as it turned out, appositely in the light of the almost simultaneous disastrous opening of Heathrow's Terminal 5.
St Davids, Pembrokeshire
Le Mesurier's wave
Sir: Presumably John Le Mesurier's "self-depreciating" wave of the hand (Last Night's TV, 27 March) became less effective each time he used it...
Sir: Well that's all my travel and accommodation problems sorted; I'm spending my summer holidays at Terminal 5 this year.