Downing Street's behaviour would be "beneath contempt" if it is playing politics over Britain's nuclear deterrent, a senior Conservative MP has warned.

Julian Lewis, chairman of the Defence Select Committee, questioned why No 10 is delaying a vote on replacing the four submarines which carry the UK's Trident weapons system.

He asked Commons Leader Chris Grayling to look MPs in the eye and reassure them that No 10 is "not playing party politics" over the issue.

Mr Lewis has already written to Defence Secretary Michael Fallon to warn of "growing concern" among MPs, contractors and their supply chains.

The Ministry of Defence (MOD) estimates that acquiring four new submarines to carry the Trident deterrent will cost £31 billion over the course of the 20-year procurement programme, with a further £10 billion set aside to meet any additional unexpected cost increases.

Speaking in the Commons, Mr Lewis told Mr Grayling: "It's one thing for you to poke fun at the leader of the Opposition over his strange ideas on Trident's successor, as you did today.

"It's quite another for No 10 to adopt this policy on the question of delaying the vote, which everybody - from the MOD, industry and both sides of the nuclear debate in Parliament - expected to be taking place in the next few weeks.

"Can you look the House in the eye and tell us that No 10 is not playing party politics with the nuclear deterrent because if they are it is beneath contempt."

Mr Grayling replied: "You have been a powerful advocate for our nuclear deterrent, it's a view I support wholeheartedly.

"You are, I think, very effective in highlighting the flaws in the Opposition's policies.

"You will know this is a matter that it's the Government's intention that it will be debated in the House in due course.

"I can't give you an announcement on when that will happen today, but I'll make sure my colleagues are aware of the concern that you raised."