Labour is trailing the Conservatives by 16 points just days ahead of a crucial vote on terror laws.

An ICM survey for the Sunday Telegraph puts the Conservatives on 42 per cent and Labour on just 26 per cent.

The Liberal Democrats are five points behind Labour on 21 per cent.

But the poll found strong public support for Prime Minister Gordon Brown's call for 42-day detention period for terror suspects, which will be put to a vote on Wednesday.

Some 65 per cent of the 1,023 adults questioned backed his plan to increase the maximum length of detention without charge from 28 days to 42.

The news came after Mr Brown made a last-ditch effort to head off a backbench rebellion over the changes.

The Prime Minister has written to every Labour MP setting out his case for extending pre-charge detention for terror suspects to 42 days.

Around 50 Labour MPs have voiced concern about the proposal - enough to inflict Mr Brown's first Commons defeat in Wednesday's vote.

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