The renewal of the Trident nuclear submarine fleet has long been a divisive political issue, here is a look at what the main parties believe the future of Trident should be.
- Labour is committed to replacing the UK's ageing fleet of Vanguard submarines which carry Trident nuclear missiles, but would consider reducing the number to three if a continuous deterrent could be maintained.
- Conservatives will pledge to renew all four submarines, Michael Fallon said.
- Liberal Democrats have said they would retain Trident but say two submarines would provide a "perfectly meaningful deterrent", while three would enable the UK to have a "continuous at-sea deterrence", Sir Nick Harvey said.
- Ukip would commit to "totally upgrading Trident" Patrick O'Flynn said.
- Both the SNP and Green party are opposed to renewing Trident.
The main political parties are wrangling over whether the UK should spend billions renewing its nuclear deterrent.
If a difference of opinion on defence didn't get in the way of the current coalition - why would it be different for Labour and the SNP?