As has been pointed out by more than one, she's dual Iranian-British so in the eyes of Iran she is only an Iranian when in Iran and that means her dual nationality means squat and UKGov get told to swivel no matter what.
And I think we're still waiting for the whining mob to explain why an "aid worker in Iran" (that was one report, iirc) was only "visiting her family", for the impression given is that she is as much an innocent in all of this as Mark Duggan was an "angel who loved old grannies and helped puppies cross the road with their shopping".
The Iranians have a lot of form when it comes to using foreign nationals to force concessions from other countries. Notably us.
They held a British businessman for about five years back in the late 80's on a pretext (Peter Cooper??) .
End-game was to get HMG to repatriate a chunk of money deposited here by the Shah's regime. Can't remember how that one resolved but IIRC the Brit was eventually released.
We still couldn't sell the Iranians anything though, cos by then the FCO had found another good reason to have no truck with them. (Basically the Yanks wouldn't like it)
But apparently it's okay for other EU nations to have extensive dealings with the Iranian regime
Envoy: Iran-Poland trade threefold
The Polish prime minister, for her part, recalled Iranians' hospitality for Polish refugees during the Second World War, and said, "Warsaw is keen to enhance all-out ties with Iran."
Italy’s Fiat to Be Back in Iran: Official - Economy news - Tasnim News Agency
" In June 2016, Iran’s leading vehicle manufacturer Iran Khodro and the French carmaker Peugeot-Citroen (PSA) agreed to launch a joint auto company in Tehran under a joint venture worth 400 million euros. "
So the British tanks, Vosper Thorneycroft frigates and Rolls Royce engined power stations we supplied them with in the 70s have gradually been replaced with Chinese, Turkish,Russian and French equivalents.
Isn't it just GREAT to have a deep and meaningful Special Relationship folks.....