Iran said earlier it hanged Alireza Akbari after he was sentenced to death for spying for the United Kingdom, prompting international condemnation.

Richard Dalton, the UK ambassador to Iran from 2003-2006, said pressure to add the Islamic Revolutionary Guard Corps (IRGC) to a list of banned terrorist organisations might have influenced the timing of Akbari's execution.

He said there were two potential reasons why the Iranian regime -- which has been shaken by anti-government protests in recent months -- may have gone ahead at this time.

"First, giving a strong message, a strong signal to their own people, and anybody else tempted to work with people whom the Iranian government regards as their enemies, should think again, because this is the kind of fate that awaits them," the former diplomat told Times Radio.

"Secondly, there's a decision pending in the UK as to whether to make the Islamic Revolution guards organisation... a terrorist organisation under British law.

"It is possible that they want to assert their right to protest against that in advance," he said

British MPs voted this week in favour of adding the IRGC to a list of banned terrorist organisations in the UK.

The motion put forward by a backbench member of parliament is non-binding on the government and ministers are still considering the matter.

Senior members of the ruling Conservative Party, including former cabinet minister Robert Jenrick, have been urging ministers to take a harder line on the IRGC.