Iranians living in Britain fear the latest diplomatic storm between London and Tehran will strain links with family back home and threaten deep-rooted business and cultural relations between the two countries.

Growing tensions over Iran's nuclear programme boiled over last week when protesters ransacked the British embassy in Iran, an attack Tehran says was carried out by angry students. Britain struck back, accusing Tehran of clear support for the attacks and expelled Iranian diplomats in London.

At an Iranian restaurant in west London, customers and staff debate the fallout of the embassy rampage, and closing of the Iranian mission in Britain, over cups of hot tea, Persian kebabs and traditional beef stew.

Fereydoon, who has lived in Britain for 22 years, visited Iran this summer, but that will be his last visit for a while for fear his British passport will be seized if he goes back.

If I go to Iran tomorrow, there's no guarantee I'll be able to come back, said the 60 year old, who like many others declined to give his surname for fear of retribution against himself or his family in Iran.

Distrust of the British runs deep in Iran, where Britain is nicknamed the old fox because of the commonly held view it still quietly manipulates international affairs. Britain's role in the 1953 coup that overthrew Iran's popular prime minister, Mohammad Mossadegh, is etched into the collective Iranian psyche.

The attack on the British Embassy, which its ambassador described as spiteful, mindless vandalism, has left many in limbo, both in Britain and Iran.

Seeking a visa, Fereydoon's uncle handed British Embassy staff his passport and the deeds to his house before the attack. Almost a week later he has no idea what has become of them in the ransacked compound.

Other practical troubles loom. One waiter said he had hoped to visit Iran in the next few months but needs to renew his Iranian passport, and does not know where to go.

If the Iranian Embassy in London remains closed, one option is for another country to host an Iranian interests section -- similar to American Iranians in applying for passports and birth certificates at the Pakistani Embassy in Washington.

Another possible solution is to use the Iran's mission in Ireland to represent Iranians in Britain.

SWORD TO A BLIND MAN

The escalation in tensions came after Britain slapped financial sanctions on Iran last month following a critical report from the International Atomic Energy Agency over Iran's nuclear programme.

Britain, the United States and other European allies suspect Iran is covertly attempting to build nuclear weapons, a charge the Islamic Republic denies, saying it wants atomic energy only for electricity and other peaceful uses.

Sitting with Fereydoon at the restaurant was Ali, who left Iran three decades ago, but remains a frequent visitor.

The 57 year old, who sells Persian rugs and antiques, said Tehran had the right to develop nuclear power, but that an atomic bomb in the hands of the Islamic Republic would be like giving a sword to a blind man.

He feared a racheting up of tensions, starting with national flag carrier Iran Air soon ending flights to Britain, though Tehran on Saturday sought to cool the diplomatic crisis.

This is just the beginning, said Ali. For all the Iranians who are here or who want to come here it's going to be a problem.

FRESH BREAD FROM TEHRAN

None of the tension between the two countries has stopped the UK remaining an attractive home for Iranian immigrants. According to the latest census data, there are now around 70,000 Iranian-born residents in Britain.

In West London, Iranian-owned shops offer express postal delivery to any address in Iran, and boast of their fresh sangak bread straight from the ovens of Tehran's bakeries.

With migration has come cultural exchange. Aliasghar Ramezanpoor, a former Iranian culture minister, now helps organize exhibitions for Iranian artists in London. He said it is going to become more difficult to secure visas for artists and permission from Tehran to showcase their work.

London is one of the most important centres for Iranian artists to sell their art and get international support to be able to continue their work inside Iran, Ramezanpoor said. When relations between the two countries go south, first of all it hurts the independent writers and artists in Iran.

Beyond the bureaucratic headaches, delayed applications and added costs, it was a sense of embarrassment that diners in the restaurant felt most keenly.

Its owner, also called Ali, pointed to the walls decorated with large photographs of Persepolis, the ruined capital of the bygone Persian empire.

I try to put nice pictures of Iran on the walls, and show people what Iran was and what it is, he said. And then something like this happens.

(Reporting By Yeganeh Torbati; Editing by Ben Harding)