The row over Trident is set to reignite after it emerged Britain has been secretly upgrading its arsenal of nuclear weapons and developed an entirely new warhead.

A report from the Nuclear Information Service revealed ministers have already authorised £85 million for the more accurate and destructive Mark 4A warhead without consulting Parliament.

According to the report, the costs and the timetable of the program have not been revealed to Parliament. David Cameron is now facing calls for an urgent vote on the issue of Trident's renewal following the EU referendum.

The independent research body said work has already been undertaken at the Atomic Weapons Establishment in Aldermaston, and new warheads have been tested at Sandia National Laboratories in the US.