Social services departments are already facing demands to support asylum seekers no longer eligible for support from the National Asylum Support Service.

Homelessness charity Shelter asked Leeds social services department last week for a community care assessment on a 28-year-old Cameroonian with severe mental health problems, who claimed asylum two days after his arrival.

The Nationality, Immigration and Asylum Act 2002, which became law last week, states asylum seekers must apply "as soon as reasonably practicable" in order to be eligible for Nass support.

Meanwhile, human rights group Liberty won an emergency injunction securing basic food and shelter for four Iraqi Kurds who had also sought help within two days of arriving in the country but were told they had not been quick enough.

The four will be given special assistance until an application for a judicial review of the new law is heard next week.

Voluntary organisations condemned the legislation and last week Labour MP Lynne Jones tabled an early day motion supporting their statement against the new law.

A Shelter spokesperson said the assessment had been carried out on the Cameroonian in Leeds, but warned it was "not a guarantee of entitlement to services". Although the council said it would provide services if the assessment revealed special needs, Shelter warned that if these needs were deemed to be the result of his current destitution and not pre-existing then he could still be denied support.

"This is just the first of many vulnerable people who we fear will be forced on to the streets by the new asylum law," said Ben Jackson, director of external affairs.

Peter Gilroy, chairperson of the Association of Directors of Social Services asylum task force, said: "This case highlights local authority concerns about section 55 [of the act]. It would seem this section was drafted with little thought as to the role local authorities might be called upon to play."

In a parliamentary answer, health minister Jacqui Smith denied that the change would result in more asylum seekers claiming to have special needs in order to gain support under the National Assistance Act 1948. She added that it was "not anticipated that from January 2003 local councils will incur additional costs".

Immigration minister Beverley Hughes added there was no reason to believe the act would lead to an increase in rough sleepers.

But the Shelter spokesperson said: "This first case shows that the government is wrong on both counts."

Meanwhile, in the High Court, Mr Justice Kay ordered urgent hearings of two test cases for the new legislation and warned the courts could face a flood of similar challenges.