One of Jeremy Corbyn's most persistent backbench critics has announced he is to stand down from Parliament to take up a job in the nuclear industry.
Jamie Reed said he will quit as Labour MP for Copeland in west Cumbria at the end of January, when he becomes head of development and community relations at the Sellafield plant in his constituency.
His departure sets up a potentially awkward by-election for Mr Corbyn in a constituency which Mr Reed had held since 2005, but saw his majority over the Conservatives shrink to 2,564 in last year's general election.
In a letter to the Labour leader announcing his decision, Mr Reed said leaving Parliament was "the hardest decision of my life".
And he told Mr Corbyn: "We desperately need a Labour government so that communities like mine can build the future they deserve.
"I wish you every success in your endeavours to become our next Labour prime minister."
Mr Reed denied that his departure was sparked by his very open differences with the party leadership.
"This decision has got absolutely nothing to do with Jeremy Corbyn," he told The Guardian. "On a personal level I've got a very cordial relationship.
"One of the reasons that I am moving on is because I think there's a better way of (serving the community) right now than to remain as a Member of Parliament."
Mr Reed was on a list of MPs hostile to the leader drawn up by Mr Corbyn's campaign team during this year's leadership election. He voted for Trident renewal earlier this year, branding the leader's opposition to nuclear weapons "juvenile" and "narcissistic".
Nuclear issues may play a part in the Copeland by-election, as the constituency includes the fuel recycling and decommissioning site at Sellafield and neighbouring Barrow is the location for construction work on the Trident replacement submarines.