I am writing this to hopefully help anyone who is getting their Iranian visa at the Iranian consulate in London. It merely represents our experience, as of July 2018 so don’t take it as gospel, but I would imagine it’s pretty representative of the experience that most people would have. I am British, my wife is American.
The first thing to bear in mind is that you must already have your authorisation code from the Iranian Ministry of Foreign Affairs in Tehran. You WILL get turned away if you don't have this. Anyone who is British, American or Canadian must go on an organised tour anyway, so most tour companies will arrange this for you as part of their service. They’ll normally apply for the code a couple of months before your trip, and it normally arrives within 4 weeks (though ours only took a week and a half!).
Once you have your authorisation code, you should print this off, and take it to the consulate, along with a completed copy of the application form (available here: http://london.mfa.ir/index.aspx?fkeyid=&siteid=234&pageid=33953), your passport, two passport sized photos, the visa fee (GBP, cash only – for British Citizens it was £170, amazingly my wife who is American only had to pay £50!), and a self-addressed special delivery envelope for the return of your passport.
The Iranian consular section (where the visas are issued) is at a different address to the Iranian Embassy itself – it is at 50 Kensington Court, London, W8 5DD. They are only open for visa processing between 2pm and 5pm on Monday, Wednesday and Friday. You cannot book an appointment – you just have to turn up. I would strongly advise, based on my experience, that you aim to be there by 1:15pm at the latest: we arrived at 1:15pm and there were already 10 people ahead of us. By the time the consulate opened, shortly after 2pm, there were at least 50 people behind us. You will queue in the street, but people were generally pretty respectful of the queue and took their place in line.
When the consulate opens, a representative will appear with a roll of numbered tickets, according to your relative place in the queue. Even if you’re travelling together, each applicant must get a separate ticket – so my wife and I had to get two between us. You then go into a pretty small room, with a few seats (nowhere near enough for the amount of people), and wait for your number to be called: it will show up on an electronic display and it will be announced over a megaphone system. Ours was called about 2:45, so you can imagine how long it would have taken to see those at the back of the queue!
Once your number is called, you go to the first window (interestingly called “window 4” – though I only saw two windows), and someone will check all of your documents and take your fingerprints. They’ll give all of your documents back to you. Once this is done, you move to the next window and hand over your documents again, they’ll get checked again, you’ll hand over the visa fee in cash, and assuming all is ok, you will receive a receipt – and you’re done. You have to leave your passports with them, with the special delivery envelope. There was a sign inside the consulate saying that they stopped issuing same-day visas as of the 1st June 2018, but we went in mid-July and they still seemed to be issuing them, so bear this in mind – especially if your authorisation code comes through with not much time to spare! I think the same-day service costs an extra £80 per application but don’t quote me on this as we did the standard service.
Despite each member of your party needing separate numbered tickets upon entry, you can go to the windows together to have your visas processed. If you both / all reside at the same address, you can also get your passports sent back in one envelope, meaning you only pay the special delivery fee once (this was an extra £7).
They say that they’ll return the passports within a week – ours came back just 3 days later, with the visas stuck in the passports. And now we’re good to go! The consulate gives the appearance of being a little chaotic, but in reality, it was incredibly organised. The whole thing took about 2 hours, including the waiting time outside of the consulate before it opened.
Hope this is helpful – if anyone has any questions, feel free to ask and I’ll do my best to answer based on our experience.