The son of a British couple detained in Iran has expressed his concern for their welfare after the UK's embassy was closed in Tehran amid the deadly crackdown on anti-regime protests.

Joe Bennett's parents, Craig and Lindsay Foreman, were on a trip around the world when they were arrested by Iranian authorities in January last year and charged with spying.

Speaking to the BBC's Newsnight programme, Bennett said the couple are in a "dangerous position" and that there was "overcrowding" in the jail due to the protests.

He added that the Foreign and Commonwealth Development Office (FCDO) told him they were still "assessing the situation".

The FCDO previously told the BBC it continued to raise the case of the Foremans directly with the Iranian authorities.

The UK government announced the the temporary closure of its embassy in Tehran on Wednesday, saying it would now operate remotely.

"We have temporarily closed the British Embassy in Tehran, this will now operate remotely. Foreign Office travel advice has now been updated to reflect this consular change," a government spokesperson said.

Britain's ambassador and all consular staff were evacuated based on a security assessment and concerns for staff safety.

Bennett said if his parents were released, they had planned to go to the British embassy.

"The trouble is, their plan was to go to the embassy, was to try to get to the embassy because they feel that that's safe ground and now... Where do they go? What do they do?" he said.

Bennett, who last spoke to his parents on Wednesday, said during the brief communication he's been able to have, they've told him of the "unsafe" and "frightening" conditions of the prison.

"There are vermin in the kitchen and in beds. It is overcrowded, it's even more overcrowding now that these protests have gone on in Tehran," he said.

He added there were "fights that break out pretty much daily" which he could hear in the background during the phone calls with his mother.

Last year, Scottish National Party MP Brendan O'Hara told the BBC the couple were being used "bargaining chips" between Iran's government and the West.

Bennett also expressed the family's "frustration" with the perceived lack of support from the government to secure his parents' release.

"I look at other nations, France for example, US, Italy, when their citizens are put in a similar situation, there's an advocacy from them at the highest level of government... and the UK haven't done that," he said.

The family just wanted the government to show "a sign of solidarity" with their plight, Bennett added.

The Foreman's legal representatives in Iran formally submitted an application for bail this week.

Both of their Iranian defence lawyers have also written to the court, stating that the pair were innocent and that there was no lawful basis for their continued detention, according to the family.

As Iran continues its deadly crackdown on anti-government protests which has killed at least 2,400 people according to a human rights agency, Bennett said he just wants to ensure his parents' safe return.

"My mum and Craig are two innocent UK citizens that are caught up in the middle of all of this. So for us, it's about their safety and prompt return home however that comes," he said.

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