Britain is committed to its Trident nuclear deterrent but wants to keep spending tight as it renews it, Prime Minister David Cameron said on Thursday after a report that the replacement of submarines could be delayed. The BBC said ministers were considering postponing the replacement of the four submarines that carry nuclear missiles until after the next parliamentary election, in 2015, to put back big spending and defuse tensions in the ruling coalition, Reuters reported. Speculation is also mounting that Trident might be downgraded to make it cheaper, for example by replacing only three of the four submarines -- which would end the policy of having at least one submarine at sea all the time. "We believe in Britain's independent nuclear deterrent, we believe in maintaining it, we believe in updating it, and the coalition agreement is very clear about that," Cameron told a news conference after an EU summit in Brussels. "But at the same time it's quite right we should ask the question 'are we getting full value for money from the renewal that will take place?'," he said. The government is conducting a strategic defence review as well as a broader review of all government spending to find savings of tens of billions of pounds as it strives to slash a budget deficit running at 11 percent of national income. Cameron neither confirmed nor denied that the government was looking at the possibility of postponing the final decision on replacing the submarines until after 2015. Earlier, his spokesman was asked specifically whether the idea of a postponement was on the table, and he said that as part of a value-for-money review, the government was looking at "the profile of expenditure", defined as "when you spend money".