The charity Oxfam has announced it will boycott the voucher scheme, and says major retailers should do the same.

I think the whole voucher system is going to be inhumanitarian and it's also going to be open to abuse

Professor David Walsh

The changes, which also include full implementation of a plan to disperse asylum seekers around the country, are being brought in under the Immigration and Asylum Act.

In total, about 2,500 are being decanted to Glasgow, which has begun accepting refugees again after a bureaucratic mix-up involving the initial influx of families.

Twelve had to be sent back to London after it emerged that they had been ordered to report weekly to a police station.

Professor David Walsh, who sits on the Refugee Council said: "My concern is that there's a need for public education.

Professor David Walsh: "Parliament should kick up a row"

"The local authority must tell people why the asylum seekers are here, what they are fleeing and who is going to pay for the programme.

"I think the whole voucher system is going to be inhumanitarian and it's also going to be open to abuse.

"The whole system has been imposed on Scotland and the local authorities by the Home Office and Westminster.

"It's not a matter of immigration and asylum. It's a matter of welfare and humanitarianism.

"Welfare is an issue that's devolved to the Scottish Parliament and I hope that the parliament kicks up a row about this matter."

Straw defends system

Home Secretary Jack Straw has rejected suggestions that the changes will reinforce prejudice against refugees, after weeks of growing controversy over begging involving asylum seekers.

Mr Straw said the reform package would not contribute to the image of asylum seekers as scroungers and troublemakers.

The measures would act as a disincentive to those trying to win residence in Britain for purely economic reasons.

Glasgow is home to refugee families

Oxfam has condemned the voucher scheme as "penny-pinching", as refugees will not be given change in cash if the value of the vouchers exceeds the value of what they are buying.

The charity's director David Bryer said: "Jack Straw must immediately remove this terrible 'no change' clause."

Asylum seekers will get �10 cash a week, and vouchers worth between �18.95 and �26.54 depending on age. Couples get vouchers worth �47.37 plus the cash.

Tories' 'simple message'

Shadow Home Secretary Ann Widdecombe said a Conservative government would make much greater use of detention in an effort to control asylum seekers' numbers.

"We will send out one very simple message," she said on BBC Radio 4's Westminster Hour.

"That message will go like this: if you come to Britain with an unfounded claim, one, you will be detained; two, you will be dealt with quickly; and three, you will be removed."

Fines for lorry drivers found with stowaways in their vehicles also came into effect on Monday, despite criticism from the drivers that they cannot be sure no-one has climbed aboard.