Gordon Brown plans to slash immigration by 35,000 a year

A new immigration Bill will set out a points-based system that will bar all but the most skilled non-EU workers from coming to live in Britain.

A specific language requirement will mean that even skilled migrants will be kept out until they can prove they have a good grasp of English.

Downing Street today refused to deny that the system could make an annual projection of the number of migrants likely to enter the UK.

Dubbed a "clever cap" by Government insiders, the scheme would consult business and other advisers to identify skills shortages.

The Prime Minister's spokesman said that if such a projection were made "that would be different from the suggestion of an overall cap".

Other late additions to the list of Bills include legislation to end the Conservatives' spending on marginal seats between general elections.

An anti-terrorism Bill will increase the period of detention without charge of terror suspects to about 50 days, while workshy teenagers will have their benefits axed and be forced to go to school or training college until they are 18.

The Tories argued that most of the speech would be a "rehash" of ideas signalled on the draft list unveiled by Mr Brown in summer.

Even Labour figures and think tanks have warned that Mr Brown needs to outline a clearer vision of his Government.

David Cameron has put Labour on to the back foot over immigration in the past week as ministers were forced to admit that official figures were much higher than previously announced.

As part of the Prime Minister's fightback, immigration has been separated from criminal justice and given its own Bill.

Crucially, Whitehall officials have revealed that the new system will effectively cut the number of foreign migrant workers by 35,000 a year.

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With non-EU migration estimated at 250,000, the change represents a 14 per cent cut. The figure is a bid to outflank the Tories' plans to set an annual cap on migration from outside the EU.

Mr Cameron has repeatedly refused to put a figure on his quota, but critics claim it will lack the flexibility required by business.

Senior Tory Sir Malcolm Rifkind hinted this weekend that the quota could not be an absolute figure and would have to be elastic.