Heathrow could slash up to £3bn ($3.98bn), or a fifth of its budget for a third runway, in a bid to win backing for its expansion, the airport's new chairman has reportedly said.

Lord Deighton said new measures would speed up the construction process by up to 12 months, while delivering more flights "quicker and cheaper."

"It's the natural next stage when you move from concept to design and delivery," he told The Times. "You think, is there a smarter way to do this? This is exactly what we did with the Olympics. Do we really need that, or is it a luxury?"

The Conservative peer, who served as commercial secretary to the Treasury for two years under George Osborne, added that among the plans up for review were proposals to build a 600m tunnel under the M25 motorway.

This would be "quite expensive" and take some time, he said, adding that they were "looking at other ways of getting to that solution", including diverting it around the airport or possibly even some form of a bridge.

A 'transit system' to carry passengers around the airport was also under review, with buses being considered instead. Constructing smaller terminal buildings was also being considered.

The third runway is projected to cost about £16.8bn, opening by late 2025.

Lord Deighton's comments were echoed by the airport's chief executive John Holland-Kaye, who said "we need to get on with it".

"Leaving the EU means that it's more essential than ever that we create trading links to the growing markets of the world and Britain controls its own trade routes," he said in a statement.

"Only expanding Heathrow, Britain's biggest port, can do this," he argued.

Their comments came weeks before Britain's prime minister Theresa May is expected to rule on the airport expansion issue, which has seen Gatwick campaign for a second runway, and proposals for a new airport in East London which were backed by the former mayor of London, Boris Johnson.

An independent commission nonetheless ruled in favour of a third runway at Heathrow.

It is thought Theresa May could give MPs a free vote on expansion as a number of her government ministers including Johnson, the Chancellor Philip Hammond and Education Secretary Justine Greening are known to be opponents of the plans for the west London airport.

On 9 September, a London Underground passenger filmed a very senior Cabinet Office civil servant holding a paper that discussed "potential waiving of collective responsibility" ahead of "the forthcoming decision around airport capacity", according to Channel 4 News. It was the second security breach of this type in a week.