"As the Defence Secretary has made very clear, we are progressing on the design and development. The decision on construction will not be taken until 2016," a Number 10 spokeswoman said.
Mr Hammond said: "The Government's position on this is very clear. We are committed to maintaining a continuous deterrent.'
Nick Clegg accused Defence Secretary Philip Hammond of "jumping the gun" on Trident as tensions grew over British nuclear-armed submarines
The Ministry of Defence has awarded BAE Systems at Barrow £315 million for ongoing design work for a Vanguard submarine replacement.