Although the UK may oppose actions that Iran has taken in the past, and while the two countries values may be very different, diplomatic engagement is essential. In an ever more connected world, the UK cannot afford to refuse conversation with powerful countries around the world. For better or worse, Iran is a major player in the Middle East. As a nation with interests in the Middle East, the UK must be prepared to have a relationship with Iran, even if it will likely remain a cool one.
We need an embassy in Iran so that Americans can have a safe place to go for services and assistance. Embassy's are needed the most in countries with volatile political situations because there is more of a chance of a citizen of another country having trouble or needing protection. Without the safety net of an embassy, American citizens would be left to fend for themselves.
Much to the dismay of saudi arabia, Iran is becoming more and more modern and westernized. Of all the middle eastern nations Iran is one of the most advanced. They even have more civil rights than our allies in Saudi Arabia. However, there is still a significant population that does not like the US.
No, it is not a good idea to reopen the UK Embassy in Iran, because there is too much of a chance that the conflict could increase and that innocent people could be hurt. Just like the situation in Lybia, they did not know that they needed more security until it was too late. The UK shouldn't risk it.