Britain's new charge d'affaires to Iran is expected to visit the country later this month amid further signs of a thawing in relations.
Ajay Sharma, previously head of the Foreign Office's Iran department, has been appointed to the non-resident post.
It comes after the UK and Iran agreed to renew direct diplomatic links during talks over the state's nuclear ambitions in Geneva last month.
Mr Sharma said: "I am delighted to take up this appointment at this important time in the UK's relations with Iran. I am very much looking forward to renewing direct UK contact with the Iranian Government and society.
"This is very much in the interests of both our countries. I hope to make my first visit to Tehran as non-resident Chargé later this month."
Significant progress is believed to have been made after Hassan Rouhani, perceived as a moderate, was elected president this summer, but the latest talks in Geneva ended without finalising a deal.
Asked about the prospects of agreement, Prime Minister David Cameron's spokesman echoed Mr Hague's view that "it can be done" despite requiring "formidably difficult negotiation".
The spokesman said Mr Cameron did not accept Tehran's assertion that France should be blamed for scuppering chances of a deal.
"What the entire E3+3 has said to the Iranian government is that they need to consider carefully over the coming days the measures that are necessary and reach the agreement that we think is possible," he said.
"It is for them to consider that very carefully over the coming days ahead of the next round of negotiations."