Frequent fliers would be hit by a new tax in an attempt to cut carbon emissions from aviation, under new plans revealed by the Liberal Democrats.

The party’s election manifesto promises to reform Air Passenger Duty to ensure that people who travel abroad frequently pay more, while holidaymakers would pay less.

The manifesto says a Lib Dem government would ”reduce the climate impact of flying by reforming the taxation of international flights to focus on those who fly the most, while reducing costs for those who take one or two international return flights per year”.

The tax rise is forecast to raise £4.9bn a year by the end of the next parliament.

The Lib Dems did not explain how they would reform the levy but hefty rises would be expected given that the entire Air Passenger Duty system raises £3.7bn a year.

While the tax would only apply to international flights, domestic flights would be forced to use more environmentally-friendly fuels.

The plan forms part of the Liberal Democrats’ commitment to making the UK net carbon neutral by 2045.

The party would also invest £20bn on boosting public transport, including £15bn on electrifying train lines and £4.5bn on restoring bus routes.

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Launching the manifesto at a nightclub in Camden, Jo Swinson said: ”For too many people, things aren’t working as they should be. We are the fifth largest economy in the world. Yet one in five of us lives in poverty. Parents working full time, on the national living wage, who are struggling to provide for their children.

“I’m not talking about trips to Disneyland. I’m talking about putting food on the table, paying for school uniforms, and keeping the heating on.”

Turning her guns on her main rivals, she said: “Boris Johnson only cares about Boris Johnson, and he’ll say and do whatever it takes to keep him in No10. This is a man who lied to the Queen, he has lied to you before and he’s lying to you now.

“And two weeks into the general election, Jeremy Corbyn still won’t tell you how he would campaign in a People’s Vote. The biggest question of the election, and he still won’t answer it. Elections are about choosing the kind of country you want to build. A man who refuses to tell you what that looks like doesn’t deserve your vote.”

The Lib Dems have committed to running a budget surplus of around 1 per cent of GDP but said they would still borrow £130bn to fund infrastructure projects, including HS2 and upgrades to schools and hospitals.

The party’s spending pledges would cost £62.3bn by 2024-25 and would be funded entirely through tax rises, including a 1p increase in income tax and a 3 per cent rise in corporation tax.

The manifesto also included a promise to legalise cannabis and raise £1.5bn a year by 2024-25 from taxing the drug.

Spending on public services would include £14bn on early years care, including offering 35 hours of free childcare for every 2-4 year old, and for younger children whose parents are in work. Funding for children’s centres would also be increased and the Early Years Pupil Premium, which helps children from disadvantaged backgrounds, would be tripled to £1,000.