If any country is justifiably paranoid, it is Iran, not the U.K. The Iranian people have been able to maintain their national integrity for 2,500 years but not easily. They have been invaded by the Romans, the Arabs, the Mongols (who slaughtered three-quarters of their population), the Russians, the British and the Iraqis.
And threats continue. The U.S. has largely replaced Britain as Iran's imperial nemesis, denying it the right to be an equal player in its home region. The Americans surround Iran with at least 15 military bases, and three U.S. allies in the region—India, Pakistan and Israel—possess nuclear weapons. As of course does the U.S. itself. And the Americans provide massive military aid to hostile Sunni neighbours of Shia Iran, such as Saudi Arabia. The U.S. has also had great success in rallying other nations to impose sanctions on the beleaguered Iranians. And if all this isn't enough, Iran is subjected to interminable threats from Israeli and American hardliners such as Benjamin Netanyahu and the contenders for the U.S. Republican presidential nomination.
Iran could escape the current peril by submitting to American hegemony, but it is apparently unwilling to do that. Another alternative of course would be to develop a nuclear weapon thereby achieving military parity with its antagonists, but it claims it doesn't intend to do that either. The siege, it seems, will continue.