The money raised will be earmarked for a new “family fund” to cut income tax for families.

A wide range of options from an increase in petrol duty to new levies on flights and firms that pollute is understood to be under consideration.

The Tories were thought to have abandoned plans to increase green taxes following criticism two years ago. However, the Telegraph has learnt that David Cameron still plans to push ahead once the economy improves.

The move will be necessary if his party is to offer significant tax breaks to married couples, seen as vital to tackling Britain’s “broken society” over the next decade. Mr Cameron will put his plans to heal the “moral” decline under Labour at the centre of his election campaign.

The plan for green taxes will not be introduced until later in a Conservative government’s first term. Although Mr Cameron has committed to recognising marriage in the tax system, he is resigned to it being largely “symbolic” until it can be properly funded.

It is understood that, initially, all married couples will be offered a small tax break while those with younger children will be given an additional incentive.

It will be paid for by spending cuts in the first years, but will become more generous as green taxes increase, a senior shadow cabinet member disclosed.

One option the Tories are understood to be considering is reintroducing the fuel-duty escalator, under which petrol duty increases by several pence more than inflation every year. It was abandoned by Labour following widespread protests over the high cost of filling up.

Last night, the shadow cabinet minister said: “We could reintroduce the fuel-duty escalator, as long as we were upfront about it. We would say the cost of petrol will rise for the next five years to reduce carbon emissions and fund tax cuts for families.

“In the same way that tobacco taxes were increased as a deliberate policy to improve health, it can be done.”

The Conservatives ultimately are thought to want to let married couples transfer their personal tax-free allowances to each other.

That would cost more than £4 billion a year, equivalent to raising fuel duty by about 9p per litre.

However, that source of funding may prove too controversial so other green taxes, including on air passengers and polluters, are under consideration. The Tory leader and George Osborne, the shadow chancellor, are cautious about discussing taxes on flights and petrol after earlier plans backfired. Some MPs fear it could lose the party votes. But the pair remain insistent that, in time, green taxes will be necessary and are considering which to increase.

The shadow cabinet minister said: “Green taxes on environmentally-damaging activities and consumption will fund our family policies in the long term. We are committed to them.”

Mr Cameron will unveil a section of the Conservative draft manifesto that will include policies to make the family stronger and address Britain’s “broken society”.

In a speech in Kent this morning he will highlight the case of two children responsible for a horrific attack on two other boys near Doncaster.

He is demanding that the full social services report into the case be released. Mr Cameron will say: “This is the moral failure of Labour’s approach. When parents are rewarded for splitting up; when professionals are told that it’s better to follow rules than do what they think is best; when single parents find they take home less for working more; when young people learn that it pays not to get a job; when the kind-hearted are discouraged from doing good in their community; is it any wonder our society is broken?

“We can’t go on like this. Labour gave us the deepest economic recession since the war – but that is more than matched by the social recession we are stuck in today.

“And though everyone hopes and expects we’re out of economic recession, unless we change the direction of government fundamentally we will never find the path to social recovery.”

Labour opposes tax breaks for married couples. Harriet Harman, the deputy leader, said the measures would not keep couples together.

“Relationships don’t work like that,” she told MPs. “The point about these tax breaks is they won’t work, but they will penalise and stigmatise.”

The Tories’ draft manifesto on the family also contains promises to extend the right to request flexible working to all parents, an idea which has alarmed business groups.

Mr Cameron will come under pressure from grassroots Tories today over his opposition to grammar schools. The issue will be raised when he debates policy on his party’s website.