Lord Jonathan Hill, the UK's European commissioner, will step down from his role following Britain's decision to leave the European Union.
Announcing his resignation on his website, Hill said he is "very disappointed" about the result of the referendum and said he doesn't believe it is right that he should carry on as the UK's top representative in Brussels.
Downing Street indicated that David Cameron will not play a role in announcing Hill's replacement, leaving the prospect the UK could be without representation at the most important institution in Brussels.
"I wanted it to end differently and had hoped that Britain would want to play a role in arguing for an outward-looking, flexible, competitive, free trade Europe. But the British people took a different decision, and that is the way that democracy works," Hill said
"I came to Brussels as someone who had campaigned against Britain joining the euro and who was sceptical about Europe.
"I will leave it certain that, despite its frustrations, our membership was good for our place in the world and good for our economy. But what is done cannot be undone and now we have to get on with making our new relationship with Europe work as well as possible."
Yesterday, Prime Minister David Cameron resigned saying it would be inappropriate to lead Brexit negotiations.
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Hill will be replaced in the highly-prized financial services brief by Valdis Dombrovskis, Latvia's commissioner and a vice president to Jean-Claude Juncker. Dombrovskis currently holds the portfolio for the "Euro and Social Dialogue", so the move was seen as significant by Brussels observers for the implications it may have over further European monetary integration.
Jean-Claude Juncker, who has called for the UK to trigger Article 50 and begin the departure process immediately, said: "It is with great regret that I have accepted Lord Hill's decision to resign. Lord Hill is an experienced politician for whom I have great respect and I want to sincerely thank him for his loyal and professional work.
"I wanted the British commissioner to be in charge of financial services as a sign of my confidence in the UK's membership of the EU. To my great regret, this situation is now changing. I have tried to convince Lord Hill to stay on as commissioner. I consider him to be a true European.
Juncker, who has been head of the Commission since 2014 and played a crucial role in the UK's renegotiation of the terms of its EU membership, added: "The work of the EU must go on."
David Cameron thanked Lord Hill for his work in a statement this afternoon, but gave no indication of who his replacement would be.
A Downing Street spokesperson said: "The prime minister is sorry that Lord Hill has decided to step down. He is extremely grateful to Lord Hill for his service at the European Commission in the crucial portfolio of financial stability, financial services and capital markets union."
However, it appeared the UK could be left without a a representative at the Commission, should Lord Hill choose to formally leave his position before a replacement has lined up, since a spokesperson for Downing Street said this afternoon:
"It will be for the next Prime Minister to decide, following discussions with European partners, what role the UK plays in the European Commission, given we remain a full member of the EU until we have left."