The transport secretary has written to his Cabinet colleague David Blunkett to express his concern at plans contained in the latest asylum bill, it emerged over the weekend.

Alistair Darling said in a leaked letter that "costly and cumbersome" proposals to force airlines to make copies of travel documents would add hours to check-in times.

The home secretary could also face a legal challenge to his decision to withdraw all state benefits from failed asylum seekers who refuse to leave the UK.

Blunkett is already being investigated by attorney general Lord Goldsmith over comments he made last week regarding a terrorist suspect.

And speaking yesterday the constitutional affairs secretary said it was "wrong" to talk in detail about the possible trial of the suspect arrested in Gloucester last week.

Lord Falconer told Sky News: "It is a matter for him [Blunkett] as to what he says. It is wrong to comment in detail in relation to the particular facts at this particular moment."