The head of MI6 has paid a secret visit to Israel to urge Prime Minister Benjamin Netanyahu not to take military action against Iran's nuclear programme, it has been reported.
The Foreign Office declined to confirm the Daily Mail report that Sir John Sawers visited Israel a couple of weeks ago with a message from David Cameron that Mr Netanyahu should allow more time for diplomatic efforts.
Mr Netanyahu stoked up international concern that a missile strike on nuclear sites in Iran could be imminent by 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."
Tehran has so far resisted pressure from the E3+3 group - Britain, the US, France, Germany, Russia and China - to give up its uranium enrichment programme, which is widely thought to be part of a drive to produce a nuclear bomb despite Iran's insistence it is intended only for civilian energy generation.
The Haaretz newspaper in Jerusalem quoted an unnamed Israeli source as saying that a high-ranking British special envoy had paid a secret visit to meet Mr 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 unco-ordinated 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.
A Foreign Office spokesman said: "We don't talk about intelligence matters or about Sir John Sawers's movements. Israel is an important partner of ours and we do speak to them all the time about a wide range of issues, obviously including Iran. We make our views very clear. On Iran, we believe that diplomacy should be given time to work."