Liberal Democrats see trimming Trident as the "mother-in-law" test of Tory commitment to the Coalition

By Tim Montgomerie

On Friday we received the confirmation that the Treasury wants the Ministry of Defence to meet the full cost of replacing Trident, Britain's independent nuclear deterrent. Defence Secretary Liam Fox had warned that such an insistence by the Chancellor, George Osborne, would seriously damage the UK's armed forces.

In an article for today's Sunday Telegraph General Sir Richard Dannatt sees Osborne's decision as having far-reaching consequences:

"This decision, if confirmed by David Cameron, is a most definite game-changer. There is no way the current defence programme can be manipulated not only to fund operations in Afghanistan, and to recover from the £35 billion overspend inherited from the previous Government, but also a Trident replacement, the aircraft carrier programme and our acquisition and operation of a host of fast jets."

In opposition, defence was Tory members' top spending priority and Cameron used the election debates to attack Nick Clegg's position on Trident renewal. ConHome understands, however, that left-wingers in the Liberal Democrat party are pressing very hard to stop a full replacement of Trident.

For them it is the "mother-in-law" test. The Conservatives, Liberal Democrats argue, have made a number of concessions to them as part of the Coalition agreement but have not yet done anything that really hurts. Likening the relationship to a marriage, one Liberal Democrat insider said that the Tories need to do something that really proves they are "sacrifically" committed to the relationship:

"Tories may have cut the number of visits to the pub but are they willing to visit the mother-in-law once a month? It's that sort of sacrificial commitment that is needed to make a marriage work."

Former LibDem leader Ming Campbell has previously accused Tory backbenchers of "priapism" every time deterrent is mentioned:

"Maybe it's the shape of the missiles but every time Trident is mentioned there is an outbreak of priapism on the Tory backbenchers. There is a real risk that the whole strategic defence review will be skewed because of the obsession with Trident. It makes no sense whatsoever to exclude Trident, the strategic deterrent, from a proper strategic review."

Liberal Democrats - along with an increasing number of defence commenters - believe that Britain does not need a "continuous-at-sea-deterrence" (CASD) and therefore does not need four new submarines. A report by the Royal United Services Institute argues that £11bn could be saved by downgrading the nature of the renewal.