Stephen Phillips, the Conservative MP for Sleaford and North Hykeham, has resigned from parliament citing "irreconcilable policy differences with the current government". Phillips announced he is to stand down with immediate effect after holding the seat in Lincolsnhire since 2010.
His decision means a by-election will now be triggered in the relatively safe Tory constituency. Phillips won the seat in the 2015 general election with more than 56% of the vote, beating Labour's Jason Pandya-Wood by more than 24,000 votes.
In a statement, Phillips said: "It has become clear to me over the last few months that my growing and very significant policy differences with the current Government mean that I am unable properly to represent the people who elected me.
"This decision has been a difficult one and I hope that everyone will respect the fact that I have tried to act in the best interests of all of my constituents."
Phillips is reported to have been a supporter of the 'soft Brexit' option and believed the UK should stay in the Single Market.
Phillips is said to have been disillusioned with Prime Minister Theresa May for not revealing her plan to leave the EU before triggering Article 50.
His resignation arrived after the High Court ruled May must consult with parliament before beginning the process of Britain leaving the EU.
In an article for the Guardian last month, Phillips wrote: "What no one who put their cross in the leave box voted for [for EU Ref] was the form that Brexit should take. It wasn't on the ballot paper and no one knew, if that were to be the result, how matters would play out."
He added: "The campaign to give parliament the right to determine our future relationship with the EU is not about reversing the referendum result. Nor is it about subverting the will of the British people, or having a second bite of the cherry. It's about the sovereignty that I and others cherish, a sovereignty that resides principally in the House of Commons and in its ability, when given the opportunity, to inform and direct the government of the day.
"Not giving parliament the chance, before article 50 is invoked, to say where it thinks these negotiations should end up is, at its core, undemocratic, unconstitutional and likely to exacerbate the divisions in our society to which the referendum gave rise. It also ignores the views of nearly half the people who voted in the referendum, who were perfectly content with our place in the EU."
Phillips's announcement follows on from former Tory Mayor of London candidate Zac Goldsmith resigning as Richmond Park MP over a disagreement with the government's plans to award Heathrow Airport a third runway expansion.
A Conservative Party spokesperson said: "Stephen Phillips has been a valuable member of Parliament since 2010 and we are sorry that he has chosen to step down. We thank him for his hard work and we wish him every success in the future."