The FCO tends to play it safe when it comes to travel advice as it goes for the lowest common denominator. Their current advice for Iran is not to go there even though it probably one of the safest places in the region albeit without access to an Embassy if things went tits up in any way. The advice had put me off visiting for a number of years to see family, but I went last year and had no problems although it was always at the back of my mind that I had no travel insurance. The FCO advice for Iran is however based on different threats than that of Tunisia and whilst I was happy to go to Tehran and wouldn't be to confident about a trip to Tunis.