UNION leaders are furious at being "double-crossed" by ministers who have decided, after a review of the asylum-seekers voucher scheme, that it will not be abolished.

The unions have long been critical of a system they regard as demeaning to asylum-seekers. But Home Office ministers privately admit that they have been unable to find an acceptable alternative. Having spent a year looking for substitute schemes, advisers have told them that to replace the scheme with cash benefits would create a "pull factor" for thousands more immigrants.

Lord Rooker, the Immigration Minister, has been told by officials: "If you have 80,000 asylum-seekers now, you would have 180,000 if we went back to cash payments."

Failure to find an alternative to the scheme will anger the powerful Transport and General Workers’ Union, whose general secretary Bill Morris described vouchers as "crude and cruel". Only the promise of the review prevented a damaging row for Labour before the general election.

Tony Blair has made clear that he has no plans to scrap the voucher scheme, and Lord Rooker’s office has failed to come up with revisions that could make it more palatable to critics such as refugee groups and the British Medical Association.

Organisations such as the Refugee Council, Oxfam, the Joint Council for the Welfare of Immigrants and Asylum Aid believe that Lord Rooker is sympathetic to getting rid of the voucher system. But he told one group last week: "My hands are tied."

David Blunkett, the Home Secretary, seems certain to refuse last-minute appeals to endear himself to delegates at the conference in Brighton by scrapping vouchers. Instead he may try to head off an embarrassing revolt by unveiling plans for a work permit system. His officials are also studying other alternatives, believed to include an increase in the value of vouchers to almost the same level as state benefits.

Mr Blunkett has instructed his officials to study the possibility of allowing some asylum-seekers to work while awaiting their fate. At the moment some doctors among the refugee community are allowed to work, but Whitehall favours asylum-seekers doing community work and being paid "in kind" with food packages rather than cash.

The package given to an asylum-seeker is the equivalent of 70 per cent of income support. Those aged 18 to 24 receive £18.95 in vouchers a week and a £10 cash voucher. A single person aged 25 or over gets a total of £36.54, comprising £26.54 in vouchers and a £10 cash voucher.

It has been suggested that there should be more lower denomination vouchers and that shops should give change; also that the range of goods available with vouchers should be extended beyond food, toiletries and clothing.

The Government has said that it will publish the conclusions of the review but has yet to reveal whether it will make public all its findings, which are believed to be highly critical of its handling of the asylum problem. Union leaders such as Mr Morris are also upset that the Prime Minister asked his own ministers to undertake the review rather than independent outsiders.

Mr Morris, who is highly critical of the voucher system, which he describes as "grotesque", is threatening to use the block vote over the issue at the Labour conference. He said: "You stand in a supermarket queue and while others have money, you have a voucher. It is a disgrace for the Labour Party."

Refugee groups have called on the Government to admit its mistake and scrap the system, rather than attempting to reform it. Alisdair MacKenzie, of Asylum Aid, said: "Why are the Government just rearranging the deckchairs on the Titanic when there is ample evidence the system is not working and is open to massive abuse? There is no evidence that if you give straight cash benefits that it is a magnet for more asylum-seekers."