The UK's nuclear deterrent should take to the skies to save £13 billion, a new report by a Liberal think tank claims.

CentreForum argues that the Trident weapons system based on submarines on the Clyde should be replaced with an airborne variety.

It claims that current set up is an "expensive and excessive" solution to the UK's nuclear deterrence requirements "even by extraordinary standards set during the Cold War".

Politicians should revisit alternatives to Trident that could free up billions of pounds for the military, it adds.

The LIb Dems have long argued that the UK's nuclear deterrent should be "scaled back".

A LIb Dem-backed Coalition Government analysis of options ruled out anything except submarines.

However, the CentreForum report points out that since the review reported in July 2013 the US has proceeded with a new air dropped nuclear weapon for NATO - the 'B61 Mod 12'.

The report argues that the UK could credibly copy the design.

It even suggests that the UK's forthcoming F-35 Joint Strike Fighters be adapted to be able to deliver a minimum nuclear deterrent.

Toby Fenwick, a research associate at CentreForum and author of the report, said: "Trident is a gold plated solution that risks the modernisation of the UK's conventional forces.

"Its advocates need to explain how they can fund their expensive system without doing irreparable damage to the UK forces.

"With no party advocating increased expenditure ahead of the election, this is a tough challenge.

"Our costed proposal provides a credible minimum independent UK nuclear force whilst providing our soldiers, sailors and airmen with the equipment they need."

Dr Nick Ritchie, a lecturer on International Security at the University of York, said: "CentreForum has produced a very timely report that challenges Whitehall's political fixation on Trident and its proposed replacement. It builds an authoritative case that if the UK remains committed to deploying nuclear weapons then it makes strategic and fiscal sense to opt for an air delivered system based on the Joint Strike Fighter."

A final "main gate" decision on the replacement of the ageing Trident system is due next year.