POLITICAN divisions over Britain's nuclear weapon-carrying submarines could be exposed today as a vote is staged calling for the defence system to be scrapped. 

Labour MPs who disagree with leader Jeremy Corbyn's views on the UK's nuclear deterrent could vote against him in the Scottish National Party (SNP) vote. 

Mr Corbyn's MPs have been ordered to stay away from the Commons lobbies instead of playing the "political game" planned by the SNP. Shadow chancellor John McDonnell blasted the debate as an "SNP stunt" following a meeting of Labour MPs in Parliament last night. 

But some Labour MPs could vote with the Conservative position of keeping and replacing Trident and the nuclear-powered submarines the missiles are based on. 

Internal tensions over the issue exploded into public view last week when it was announced Mr Corbyn had appointed former London mayor Ken Livingstone as a "co-convener" of a party defence review alongside shadow defence secretary Maria Eagle, who supports Trident. 

Official Labour policy remains firmly supportive of the deterrent despite Mr Corbyn's strong personal opposition. The SNP opposition day motion is due to be called to a vote sometime in the late afternoon. 

The motion - which is sure to be defeated by the Government - would have no legal force even if it were successful. Prime Minister David Cameron announced yesterday the cost of replacing the ageing Vanguard-class subs could rise to £40 billion. 

Yesterday's Strategic Defence and Security Review (SDSR) revealed the Government had decided to ditch the traditional single main gate decision - when the final go-head is given to a major project - in favour of a "staged investment programme". 

The document committed the Government to a debate in Parliament on the principle of continuous at-sea deterrence - which requires a minimum of four boats - and the Government's plans for the future fleet of subs. But it made no such commitment on a vote, sparking speculation over the possibility that MPs would be denied a chance to express their views. 

However, Mr Cameron told the Commons during a debate on the SDSR: "The main gate decision, we will be moving ahead with the four submarines and obviously at the appropriate moment we'll want to have a vote in this House."