Foreign Secretary William Hague said the nuclear deal with Iran does not mean the UK embassy in Tehran will reopen.
"We have to be clear with Iran that an embassy, if we reopen it, would be able to operate properly with all the normal functions. We will take this in a step by step way," he said.
When you consider the diplomatic mountain the US and Iran have already scaled, you get a daunting sense of the challenge ahead.
The deal between Iran and world powers looks like a breakthrough, but with six months of wrangling over details ahead, it could still fail.
The nuclear agreement between Western powers and Iran was broadly welcomed by politicians, former world leaders and Middle East experts.