LONDON Iran is downgrading its relations with Britain by not replacing its outgoing ambassador to London, Rasoul Movahedian, when he leaves in the next few weeks, diplomatic sources said on Thursday.

Last year, Tehran nominated former deputy foreign minister Mehdi Safari to take up the post but changed its mind earlier this year, sending him instead to Beijing as ambassador to China, which has emerged as Iran's principal backer on the world stage. A UK Foreign Office spokesman said “We are aware that Mr Movahedian is leaving, but we have not been made aware of any plans to replace him.”

Iran's decision not to replace its ambassador follows a year of worsening relations with Britain. Ties have been fraught since the 1979 Islamic revolution, but have plummeted since the disputed presidential election in June last year and the subsequent opposition protest, which Tehran accused Britain of orchestrating.

Iranian staff at the British embassy in Tehran were detained and warned not to return to work. The embassy's chief political analyst, Hossein Rassam, was sentenced to four years in prison for allegedly fomenting anti-government protests and is now out on bail. Britain has also been castigated for supporting UN sanctions against Iran over its nuclear programme and there have been calls in the Iranian majlis for bilateral relations to be downgraded.

One of the country's vice-presidents, Mohammad-Reza Rahimi, last month called the English “a bunch of thick people ruled by a mafia”.

There was no comment on Friday from the Iranian embassy on Movahedian's replacement. On the embassy website, a folder labelled “bilateral relations” was empty. However, there has been no formal announcement by the Iranian foreign ministry on the status of bilateral ties.

“This could be a bureaucratic blockage that amounts to a decision,” a British diplomatic source said.

“We haven't heard anything since the Safari debacle. It could be that the president is refusing to agree a replacement for Movahedian, or it could come from the (supreme) leader's office.”—Dawn/Guardian News Service