Government departments are to co-operate with one another and with police, local authorities and health care trusts to deny illegal immigrants access to work, benefits and services in the UK.

Home Secretary John Reid has announced a new enforcement strategy designed to "block the benefits of Britain" to those in the country illegally.

But the "get tough" policy was branded unrealistic and inhumane by campaigners, who said it threatened to leave up to half a million people destitute, forcing many into crime or the black economy.

The Joint Council for Welfare of Immigrants called for the "regularisation" of those in the country for more than two years, arguing that allowing them to work legally would provide more than £3 billion in tax revenue for the Treasury.

The Home Secretary said that the new enforcement drive was based on "fairness and enforcing the rules" and would allow the Immigration and Nationality Directorate (IND) progressively to deny work, benefits and services to those in the UK illegally.

Measures include a "watch list" of illegals to alert Government agencies if someone applies for services to which they are not entitled, workplace enforcement teams to track down bosses employing people who should not be in the country, and pilots in three NHS Trusts to use IND data to ensure migrants pay for care where required

Immigration crime partnerships will be created between IND, local authorities, police, HM Revenue and Customs and local agencies to detect those here illegally and block benefits. Landlords could be fined up to £20,000 for housing illegal immigrants in overcrowded flats. And new systems could be put in place to identify illegals fraudulently applying for driving licences.

Mr Reid said: "Most people who come to this country wish to comply fully with our immigration laws, but where they don't we are committed to blocking the benefits and privileges that should only be enjoyed by those here legitimately. That's why the time is now right to tackle the root cause of the problem - exploitation.

"We have to tackle not only the illegal trafficking but also the illegal jobs at the end of the journey. Introducing biometric ID cards, starting with newly-arrived foreign nationals, will make it easier to ensure fair access to services and stamp out fraud and abuse."

He added: "This new approach will make life in this country ever more uncomfortable and constrained for those who come here illegally."