Rachida (not her real name) was playing badminton in a Blackburn sports centre when I asked her if she'd talk to me about politics. I was making a Beyond Westminster programme for Radio 4 about how British Asian voters were deserting the three main parties. This young woman was initially very reluctant to contribute, and when she saw a middle-aged, male Labour councillor from her community trying to eavesdrop, she begged me to send him away.

But once he had gone, she opened up. British Asian politicians in Blackburn (and they're almost all Labour), she said, had imported practices from Pakistan and India. Some did favours in return for votes. Some were sexist. They didn't have the interests of the whole community at heart. Worst of all, they put serious pressure on British Asian women to vote for them.

"Has anyone ever asked you to fill in a postal vote or to give them your postal vote so they can fill it in for you?" I asked.

"I think that's common practice in Blackburn, if I'm being honest," she said. Had it happened to her? "Yes."

Bravely, she had resisted. But this was a confident, articulate British-born woman, who had the strength to defy the local bully-boys when they tried to pressurise her into voting for them. And she was still scared enough of their reaction to ask me to use a false name in the interview. So imagine how hard it must be if you are newer to Britain, or less sure of your rights,and your husband, father or local councillor puts a postal ballot in front of you and says "Sign here".

Most people see postal votes as a convenient way of avoiding the traipse to the polling station on a working day. Since Labour liberalised the law in 2000 to allow postal voting on demand, the number of people using them has soared. In the 1997 election, it was just over 2 per cent. By 2005, it was 15 per cent (and double that in Blackburn). There is no official figure for the 2010 election, but some constituencies reported increases of 200 per cent in postal vote applications. And this was particularly true in seats with a large Asian-heritage population.

Almost all the worst instances of postal vote fraud since 2000 have happened in seats with large south Asian concentrations, such as Oldham, Blackburn and Tower Hamlets. In 2004, Richard Mawrey QC, presiding over an election court, found six British Asian Labour councillors from Birmingham guilty of corruption that would, he said, "disgrace a banana republic". He declared that the Government's introduction of postal voting on demand was "an open invitation to fraud".

One of the biggest problems with postal votes is that they don't guarantee you a secret ballot. What use is the privacy of your own home if you have to fill in the form with your husband or father looking over your shoulder? Or if you are allowed only to sign the form, but have to hand it over to him to cast the vote? The great thing about a polling station is that no one is allowed to enter the cubicle with you. I was once even stopped from bringing a child in with me who wanted to see democracy in action.

So far, most of the complaints about postal vote fraud have centred on phantom voters: two-bedroomed flats with supposedly 15 people living in them, all of whom opt to vote by post. Because the registration form only has to be filled in by the head of the household, and few other checks are made, it is "childishly simple" to cheat in the British system, said a Council of Europe report in 2008.

But a Joseph Rowntree Reform Trust report in the same year drew attention to other problems with postal voting in Asian-heritage areas. It observed that the Biraderi tradition of clan politics that has been imported into many communities from the Asian sub-continent lent itself to the delivery of block votes to a party. Sometimes these postal ballot papers are taken to "voting factories", to be filled in by party activists. Biraderi is a practice that infuriates young British Asian voters, particularly women, as I saw in Blackburn, and as the whole country saw in the Bradford West by-election.

Postal votes used to be granted only if voters could show they were unable to get to a polling station. A Home Office Working Party warned in 1994 that "a move to absent voting on demand might increase the opportunity for fraudulent applications to be made without the knowledge of the elector. On balance, we consider that the risk of increased fraud outweighs the potential advantage for the electorate of making absent voting available to all". But Labour went ahead regardless.

And even the police think it's a bad idea. A report to the Metropolitan Police Authority by the Assistant Commissioner for Specialist Operations spelled it out in 2006: "Anecdotally, some community contacts have remarked on how practices that are seen as acceptable outside the UK have been adopted in respect of UK elections – for example, the head of an extended family instructing members to vote for a particular party or candidate. Postal voting increases the risk, as the safeguard of a truly secret ballot is removed."

This government plans to deal with the phantom voter problem by bringing in individual voter registration in 2014. Under the new system, the head of a household won't be able to register all the people living (or not living) under one roof: voters will have to do it individually and provide dates of birth and National Insurance numbers so their identity can be verified.

But this does nothing to prevent coercion, particularly of women. What we need to do is to go back to the system that used to prevail – whereby postal ballots are granted only to people who physically can't get to the polling station.

It might be a slight inconvenience for some voters. But it's only right in a democracy that everyone should be protected by a secret ballot. And you don't even have to feel sorry for Rachida and her sisters to want the law changed. In those constituencies with a high percentage of postal votes, it's scarily easy for a result to be stolen. If the next election is anything like as close as the last, it's quite possible that the next government could be decided by dodgy postal votes.

There's still time to clean up the system by 2015. Nick Clegg should tighten up the rules on postal voting in the same legislation that he is bringing in for individual voter registration. It's not just the women of Blackburn, Bradford and Birmingham who need it. So does the health of our democracy and our reputation in the world. After all, who wants to live in a banana republic?

m.sieghart@independent.co.uk / twitter.com/MASieghart