EXPANDING Heathrow or Gatwick will be a “boon for Scotland” for decades to come, David Mundell insists today as he and his cabinet colleagues prepare to make a crucial multi-billion pound decision tomorrow on which airport expansion option should be chosen.

Writing in The Herald, the Scottish secretary, who sits on the special cabinet sub-committee which has been examining the issue and will decide on the preferred option, notes how the continued growth of Scottish airports will be vital to the process of growing Scotland’s economy.

“But they alone can’t provide the connectivity Scotland needs. Only a London hub can do that; linking Scottish businesses with fast-developing cities in China, India, and South America, that will be the gateway to growth in the 21st century.

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“Scotland is responsible for some of Britain’s leading exports and access to a major hub airport is going to become even more important in the future if those exports are going to increase,” he argues.

The secretary of state stresses extra capacity will mean "better air links between Scotland and London, an opportunity to launch new routes, and more competition between airlines, putting downward pressure on air fares".

He notes while other countries have plenty of runway capacity, Britain has not built a new one since World War Two and warns that the longer a decision is put off, the greater the cost will be.

Noting how the UK Government is determined to make Brexit a success, Mr Mundell adds: “That means not just taking back control from Europe but securing Britain’s future as one of the best connected countries on earth. By building new runway space in the south east of England, we will achieve that objective and the whole of Scotland will profit.”

After years of swithering, the UK Government will decide between either: a new third runway at Heathrow airport to the west of London; extending one of the current runways to double it in size or to build a second runway at Gatwick airport in Sussex.

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In 2009, former Prime Minister David Cameron famously declared that “no ifs, no buts” there would be no third runway at Heathrow. But a review his government commission came out in favour of the west London option last year.

Depending on which of the three options is chosen, the cost is estimated to be anything up to £20 billion. The Scottish Government has already backed expanding Heathrow, saying this offered significant strategic and economic benefits for Scotland, including the creation of 16,000 new jobs.

SNP sources have made clear whichever scheme is chosen, Edinburgh should get millions of pounds as a result of the knock-on financial effect through the Barnett Formula.

The UK Government has made clear that following this week’s decision a public consultation will take place. A parliamentary vote is expected around the end of next year.

But a legal challenge seems certain whichever option is selected. This would threaten to delay the process for years. It is suggested that on Tuesday Mr Mundell and his colleagues on the cabinet sub-committee will be presented with plans to offer residents near Heathrow a "world-class" compensation package, including a 25 per cent added premium onto the market value of their homes should they have to be demolished.

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In what appears to be a move to prevent resignations from the cabinet, Theresa May has suspended collective responsibility and will allow some frontbench colleagues to air their objections to whichever scheme is chosen for a certain, undisclosed period of time.

Boris Johnson, the foreign secretary, who has been a bitter opponent of expanding Heathrow, once said he would lay down before the bulldozers if the west London option were chosen.

Chris Grayling, the transport secretary, insisted yesterday that, despite strong rumours that the UK Government had come down on expanding Heathrow, no decision had yet been taken.

He told the BBC’s Andrew Marr show: "Genuinely, it's going to be a decision on Tuesday and it's a difficult one, because all three of these are well-crafted proposals and any one of them could bring benefits to the UK."

The ministerial decision on Tuesday is expected to be followed by a Commons statement.