In the past fortnight there has been an unprecedented wave of demonstrations with about 250 immigrants in more than 10 institutions joining hunger strikes.
The sharp rise in the number of people incarcerated has also forced the Home Office increasingly to use jails to hold asylum seekers - none of whom have committed a criminal offence. This development was fiercely attacked by the Chief Inspector of Prisons earlier this week and was blamed for a rise in suicide attempts.
Civil rights and immigration groups are extremely critical of the length of time unconvicted asylum seekers are being detained while their applications are assessed. More than 10 per cent have to wait more than six months; some have been held for almost two years. The delays are often caused by a massive backlog of applications: there are more than 45,000 people waiting for a decision.
Pressure caused by the rise in asylum-seeking detainees - there were 375 in December rising to 720 this month - spilled into protest on 11 March when a dozen detainees at Campsfield House detention centre, near Oxford, began a hunger strike. The protest quickly snowballed and at one stage more than 130 of the centre's 200 inmates were refusing to eat. Ringleaders who were considered 'disruptive' were sent to prisons, several people have been taken to hospital, and special medical supervision has been introduced. Detainees have complained that staff have used intimidatory tactics, such as turning off heating, delaying post and access to solicitors, to try to get them to eat.
The hunger strike has spread to other centres and prisons, noticeably Haslar dention centre in Gosport, Hampshire, Winson Green prison, Birmingham, Canterbury prison and Harmondsworth detention centre, near Heathrow.
The number of hunger strikers has declined; several people have been released, hospitalised or deported, others have given up voluntarily. However, there remains a hard core of protesters who have vowed to continue, with a few now refusing liquids as well as food. Yesterday there were 130 still on hunger strike in 10 jails and centres, with 60 at Campsfield.
The heart of the protesters' complaint is the 1971 Immigration Act which allows people to be held indefinitely without charge and with little or no recourse to bail. A change in law last year, which was supposed to speed up some applications, has resulted in more people appealing and further delays.
From 1984 to 1988 there were fewer than 20,000 applications. In the following five years this rose to 130,000. Only a tiny proportion of the applicants are detained and not all immigrants held are asylum seekers. In February there were 950 people held under the Immigration Act. Between 60 and 80 per cent are usually seeking refugee status. The remainder are illegal entrants, people who have overstayed their work permits or who have no permits, those whose visas have expired and inmates awaiting deportation after serving sentences.
There are about 450 places at the seven detention centres in England and Wales. Most detainees are kept at Campsfield which has 200 places. Harmondsworth has 95, and Haslar - a former prison - 120. Small numbers are kept at detention centres at Heathrow, Gatwick, Stansted and Manchester airports.
The remainder are kept in prison. In March, asylum seekers were scattered throughout the country in more than 40 jails and young offenders' institutions.
The use of prisons for this purpose was severely criticised this week by Judge Stephen Tumim, the Government's Chief Inspector of Prisons, who said new accommodation should be found urgently for 'distressed, despondent and in some cases desperate' immigration detainees held at antiquated Pentonville jail in north London. There are about 60 immigration detainees there.
He said: 'We have grave reservations about the appropriateness of holding such inmates in a busy local prison.'
He added that the average time for an immigration detainee to get a decision was six months.
The Home Office argues that in some cases prisons are the best places to detain asylum seekers, particularly if they have medical or psychological problems. Jails, unlike detention centres, have hospital wings. However, Judge Tumim said medical facilities at Pentonville were 'grossly inadequate'.
A Home Office spokeswoman said: 'We are constantly reviewing decisions to detain, and we only detain when there is no alternative and where there are grounds for believing that the person concerned will not comply with any restrictions imposed.'