Britain must replace its nuclear deterrent, the Conservative Party says.
Liam Fox says other countries are still trying to get nuclear weapons
Shadow Defence Secretary Liam Fox said the UK must maintain its four Trident missile submarines "for as long as possible" before replacing them.
Dr Fox told the BBC a new deterrent was needed because it was the best way to ensure no other country launches a nuclear strike.
His comments came days after MPs began an inquiry into Trident, which is expected to be obsolete by 2020.
"We have to replace [Trident] because there are states in the world still trying to get nuclear weapons," said Dr Fox.
"The best guarantee of them not being used is for Britain to have an independent deterrent."
The House of Commons defence committee is taking evidence from a range of experts about the type of threat the UK might face in 20 years' time.
The cost of replacing the UK's four submarines armed with Trident missiles could reach £20bn, according to some estimates.