In a move which could put his party at odds with its Conservative coalition partners, the Chief Secretary to the Treasury admitted Britain faces a "big decision in 2016" over alternatives to the current weapon system.
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PM spokesman's comments come following reports that the EU is secretly drawing up plans for greater military cooperation across the EU.
The Labour politicians put their alleged differences aside to jointly highlight how remaining in the EU could help fight climate change.
Late sunshine here and there this evening - but more cloud for southern Scotland, northern England and Northern Ireland again.