Foreign Office minister Mark Simmonds has resigned from the Government and will stand down at the next election in a fresh blow to the department following the departure of Baroness Warsi in protest at the Government's policy on Gaza last week.
Mr Simmonds, who is the MP for Boston and Skegness, said the decision was agreed "some weeks ago" but the announcement had been delayed to allow him to chair a United Nations session on the situation in the Democratic Republic of Congo.
He stated that the decision to step down was not related to events in Gaza and in his resignation letter told David Cameron he would "remain supportive of you, your Government and the Conservative Party".
In a statement, Mr Simmonds said it had been a "huge pleasure and a privilege" to serve his constituency.
But he said: "Despite the enjoyment and personal fulfilment I have found in this role, the lack of support available to MPs with families outside of London and the sacrifice to my family life, has become intolerable. At this stage, I need to focus on providing for my family."
Mr Simmonds said he was proud of his work while a Foreign Office minister, adding: "I am exceptionally proud of the achievements this Government has made in reducing the deficit, increasing employment opportunities, investing in the NHS and reforming our welfare system.
"I only hope that these significant improvements can be built upon after the 2015 general election by a majority Conservative government.
"I remain supportive of the Prime Minister, his Government and the Conservative Party.
"I know that my Conservative colleagues in Parliament will do everything possible to secure a majority government after the next election to deliver further reform, economic progress and the all-important in/out EU referendum.
"I will of course continue to serve my constituents in Boston and Skegness to the best of my ability until May 2015. My decision will not alter my role as their local member of Parliament."
In a separate statement to his constituents Mr Simmonds said that "despite the enjoyment and personal fulfilment I have found in this role, the lack of support available to MPs with families outside of London and the sacrifice to my family life, has become intolerable".
"At this stage, I need to focus on providing for my family."
The Prime Minister said Mr Simmonds still had "much more to give" and had been an "incredibly loyal colleague, but also a good friend".
He will be replaced at the Foreign Office by Tory MP James Duddridge.