Conservatives will share the proceeds of a £1bn tax on banks between one earner married couples and cutting the deficit

Overnight the Tories announced the details of their long-awaited pledge to back marriage in the tax system.

Four million of Britain's twelve million married couples will benefit from a commitment to allow basic rate taxpayers to transfer part of their tax allowance. The commitment will benefit one-earner couples by up to £150-a-year and its £550m overall cost will be financed by a £1bn levy on banks. The rest of the bank levy will be used to repay debt.

A poll in the Daily Mail finds 65% of voters supportive of the raising of tax allowances for married couples.

The Daily Mail gives the policy an enthusiastic welcome in its leader column:

"The Mail congratulates Mr Cameron on a courageous move, supported by two thirds of voters in our poll today. He deserves the wholehearted backing of everyone, married or single, who recognises the traditional family as by far the most effective and humane welfare system known to man."

The FT is less convinced:

"The move will be welcome to 4m families. The decision to fund the tax break from a levy on banks also looks like astute politics, showing the Tories on the side of the ordinary family rather than high earners. But the £150 break is too small to change behaviour, either in favour of marriage or staying at home to bring up children. Given the state of the public finances, it may be an expensive political gesture."

Interviewed on the Today programme, David Willetts MP - who co-ordinates family policy for the Conservatives - outlined some of the key advantages of the policy.

• It is focused on one earner couples and is designed to address the problem of households where one spouse works and pays a lot more tax than a household where two people work but earn the same money.
• Nearly every other nation in the world recognises marriage. Britain, Willetts said, is very unusual in treating people as individuals in the tax system, ignoring their family status.
• It is an affirmation of a public commitment - a small sign from society that marriage is a good thing.

This commitment will infuriate the Left and Vince Cable and Ed Balls have taken to the airwaves this morning to condemn it.

Tax has become central to the election battle. The first week of campaigning has been dominated by the Conservatives' NI pledge. This marriage tax announcement will join the lengthening list of other Tory commitments on tax.

Matthew Parris speculates this morning that the Conservatives may need to be stronger in ruling out a rise in VAT. He warns that voters' fears of Tory intentions on VAT still has the potential to derail the Tory campaign.

Tim Montgomerie