New aircraft carrier is a key part of UK's defence infrastructure

It is, the Labour leader said, “wonderful” but “massively expensive”.

At a cost of £3 billion, the vast new vessel becomes one of the most important parts of Britain’s defence infrastructure.

Mr Corbyn, in a sign perhaps of him sending out moderate political signals now that he thinks Downing Street is within reach, was careful not to say that the entire project of commissioning and building HMS Queen Elizabeth had been unnecessary.

He was positive about the scheme but gently queried the expenditure.

While the costs of all major publicly funded construction projects are deserving of close scrutiny, particularly given the way in which the largest such projects almost invariably go over budget, this was a ship that needed to be built.

It is the UK’s largest ever warship.

As Theresa May said yesterday as she visited the boat, it is a symbol of the UK as a “great global maritime nation”.

This country acquired that reputation by being a wealthy island, in which access to the seas was always easy.

While the global security threat is ever evolving, and while traditional components of Britain’s military capability such as aircraft carriers and an independent nuclear deterrent will be of little use for some of the security challenges ahead such as domestic terrorism, the country cannot dispense with such defences.

Or not if it wants to remain a leading global power with a permanent seat on the UN Security Council.

The UK is one of the few European countries to meet the Nato target of 2% of GDP spent on defence.

This commitment is all the more important as Britain prepares to go it alone outside the European Union, and stand alone as an influential nation.