Hammond said it was for the U.K. government to begin the process of leaving the EU by triggering Article 50 of the Treaty of Lisbon, the formal mechanism for ending membership, but said the departure would not begin until Prime Minister David Cameron’s successor takes office.

Britain’s governing Conservative Party is in the process of electing a new leader following Cameron’s resignation after last month’s referendum result for Brexit.

Hammond told the House of Commons foreign affairs committee Thursday: “It will be for the new prime minister to decide how best to engage with the European Union and to express to the European Union our views as a government about how we should move forward. This is an untested process. Nobody has ever done this before.

“In terms of triggering Article 50, my judgment is it wouldn't be in the best interests of the U.K. to trigger Article 50 immediately.

“Article 50 sets a clock ticking and I don't think at the moment, for various reasons - not least of which, we don't have the new prime minister in post - for the moment we are not in a position to begin substantive negotiations immediately and therefore it would be unwise to start the process ticking by triggering Article 50.” 

Almost 52 percent of British voters rejected their country's 43-year EU membership in the referendum held on June 23.