A senior MI6 chief paid a secret visit to Israel in order to urge the country not to take military action against Iran over its nuclear programme, it was reported on Wednesday.
The Foreign Office declined to confirm the Daily Mail report that Sir John Sawers visited Israeli prime minister Benjamin Netanyahu recently with a message from David Cameron that Mr Netanyahu should allow more time for diplomatic efforts.
On Tuesday, Netanyahu did nothing to calm concerns that a missile strike on nuclear sites in Iran could be imminent, saying: "The world tells Israel 'wait, there's still time'. And I say, 'Wait for what? Wait until when?' Those in the international community who refuse to put red lines before Iran don't have a moral right to place a red light before Israel.
"Now if Iran knows that there is no red line. If Iran knows that there is no deadline, what will it do? Exactly what it's doing. It's continuing, without any interference, towards obtaining nuclear weapons capability and from there, nuclear bombs."
Iran has not buckled to pressure from the E3+3 group - Britain, the US, France, Germany, Russia and China - to give up its uranium enrichment programme, which politicians consider to be part of a drive to produce a nuclear bomb despite Iran's insistence it is intended only for civilian energy generation.
Israeli newspaper Haaretz quoted an unnamed Israeli source as saying that a high-ranking British special envoy had paid a secret visit to meet Netanyahu and defence minister Ehud Barak, as well as a number of security and diplomatic officials, and deliver a "stern message" from Mr Cameron.
The source said the envoy warned against "an uncoordinated Israeli strike on Iran at this time" and stressed that Britain believes there is still time for diplomatic measures to work.
The envoy - identified by the Mail as Sir John - reportedly suggested that economic and diplomatic sanctions on Iran could be toughened up if it continues to resist international pressure.
The unnamed source said British fears about an imminent strike had been heightened by Mr Netanyahu's failure, during a phone conversation in July, to provide clear answers to Mr Cameron's questions about his intentions towards Iran.
Haaretz reported the unnamed source as saying that pressure from the UK, US and Germany had cooled Mr Netanyahu's enthusiasm for an uncoordinated military strike on Iran.
Wary of causing a rift with some of his country's closest allies, the Israeli PM was now pushing for international "red lines" on Tehran's nuclear activities, said the paper.