The report found that the employment of illegal immigrants to care for the elderly was "widespread" and "significant" following investigations into 110 suspected cases.

Officials discovered that those employed included a suspected murderer and other criminals, it said.

Shadow home secretary David Davis called for the report to be published immediately and claimed the Home Office had "turned a blind eye" to the situation.

Home Secretary Jacqui Smith, asked repeatedly in an television interview if illegal immigrants were employed now in care homes, refused to answer directly. She instead insisted the changes the Government was making to the immigration system would "minimise" the ability of people to come to the UK and work illegally.

But The Sunday Times, which obtained the report, said officials had complained that the findings had been largely ignored.

Mr Davis told Sky News: "The real problem was that the Government was willing to turn a blind eye to known illegal immigrants in what looks like as many as half the employees in some care homes. The people in these care homes are some of the most vulnerable people in the country...it is putting many vulnerable people at serious risk.

"What should have happened is that they acted directly on the problem - not talk about the rhetoric of ID cards and biometric visas which will make no difference to this whatsoever."

Ms Smith told BBC One's The Andrew Marr Show: "I think what people will want to know is that we responded to that report two years ago and that we are making the changes in the system that will minimise the ability for people to come here illegally, to stay here illegally and to work here illegally and that is what we are doing."

But put to her that she "couldn't know" what the present situation was she said: "By definition you do not know if somebody is here illegally. But what we do know is that we are making the reforms to tackle that."