Chancellor Alistair Darling is expected to announce the replacement of air passenger duty with a tax on flights in today’s budget.

Darling is expected to deliver the greenest budget yet, with the new flight tax intended to help cut carbon emissions.

The chancellor is also expected to announce a tax on gas-guzzling four-by-fours and on plastic bags.

It is anticipated that a 2p fuel duty due to come into affect on April 1 will be delayed for six months, following pressure from motorists’ groups and green campaigners.

Mr Darling’s budget speech will begin at 12.30pm. He will speak for an hour in the Commons, with responses from Tory leader David Cameron and Lib Dem leader Nick Clegg.

See for the full report later today.