Ali Rahmi, 21, pleaded guilty at Southwark crown court to one count of arson on September 29, 2008. He had drenched the armour-plated front doors of the embassy in petrol and set them alight with a cigarette lighter.

No-one was hurt in the incident, which the court heard came just days after Rahmi received news that a relative had been killed in Iran.

Rahmi himself had arrived in Britain two years earlier seeking asylum, claiming Iranian security forces had tried to kill him. His request was refused but he appealed and the case was under review at the time of the attack.

Prosecutor Peter Zinner told the court that the attack was a "venting of anger... a totally irrational outburst of violence to protest against what he perceives to be his mistreatment".

Judge James Wadsworth said it was a "clearly serious crime" but he would spare him immediate imprisonment because of his experiences.

"However, because this was such a betrayal of your position in this country, there must be a sentence of imprisonment, although the 50 weeks I am imposing will be suspended for two years," he said.

The embassy, in the affluent London district of Knightsbridge, was the scene of a siege in 1980 when it was taken over by Iranian Arab separatists.