An MP who resigned as ministerial aide to cabinet minister Peter Hain over renewing the UK's nuclear weapons says it was a difficult decision to take.
Chris Ruane had never previously voted against the government
Vale of Clwyd MP Chris Ruane was the fourth government figure to step down over the renewal of Trident submarines.
He gave up his post as parliamentary private secretary to Wales and Northern Ireland Secretary Mr Hain.
In his resignation letter to Mr Hain, he said: "This is not a decision I take lightly."
Mr Ruane told Mr Hain he was unable to support the government's proposals.
He wrote: "I am not a unilateralist, but I do hope that the world can work towards the reduction of nuclear weapons."
He was among 95 Labour MPs who voted to delay a decision on Trident.
The government won the day with Conservative support.
In his reply, Mr Hain said he regretted his resignation, adding: "I understand and respect it, and I welcome the measured way in which you have carried out your decision."
"I know how difficult this decision was for you. You have never voted against the government in 10 years.
"Despite your decision to step down, I know that you will remain one of the most vocal and loyal supporters of this Labour government and the progress that we have achieved, both in your constituency and beyond."
Mr Ruane, a 48-year-old former teacher, became an MP in 1997. His majority at the last election was 4,669.
Tony Blair argued that it was "essential for our security in an uncertain world" that the UK began the plan to renew Trident as soon as possible.
Conservatives called the plan "sound and sensible," but Liberal Democrats, who wanted a decision delayed, said the vote was "a humiliation for the prime minister".