I thought I would share my experience at the recently re-opened Iranian consulate in London:
I went down yesterday afternoon to speak the nice man at the counter (having spent hours trying to get hold of them on the phone, with no success) to ask about whether British nationals still need to go on a guided tour. He confirmed that they do not, but that I would need a visa authorisation code, unless I knew somebody living in Iran. I asked, just to clarify, if I, as a British citizen, needed to be escorted by a guide or local whilst travelling in Iran. He said that I did not.
The consulate is not in the same building as the embassy, but at 50 Kensington Court (about 10-15 minutes walk to the west). It is open from 2-5 p.m. on Mondays, Wednesdays and Fridays.
So, the next question is, how best to get this authorisation code? I'm sure that there will be plenty of companies who will try to insist on selling some kind of tour, in order to obtain this, but the man at the consulate seemed pretty clear that it was only the authorisation code that they were interested in.
I hope this sheds some light on the situation for those of you who were wondering about this.

