Rasoul Movahedian-Attar began his tenure on Tuesday.
He was welcomed by a representative of the British Foreign Ministry.
The post in London had been vacant since late 2005 when hard-line Iranian President Mahmoud Ahmadinejad recalled 40 of the countrys ambassadors and envoys as part of a purge of the Islamic Republics diplomats who did not belong to the ultra-Islamist faction.
Movahedian-Attar was previously Tehrans top envoy to the Czech Republic, Slovakia, and Portugal.