I had my K1 interview yesterday at the U.S embassy in London and we were approved and have now entered administrative processing! My experience was similar to what the majority of others have described as simple, speedy and a tad anti climatic. I expected cake and confetti.
As I don't have anything to say that hasn't already been said about the process I will summarize.
The interview is a breeze. You have nothing to worry about if you go prepared.
Overall I was asked to provide my:
1) Passport
2) Ds160 confirmation page
3) Affidavit of support (I-34) with supporting evidence (Ronnie's last year tax returns and W2).
4) Birth certificate
5) Deed poll (only needed if you have changed your name which I have)
6) Acro (less than a year old)
7) One passport photo (mine was US size)
8) Fingerprints (they take them there)
They had my results from the medical I underwent on the 20th of February and handed over a CD containing my x-ray for POE. I would advise leaving 2 weeks between medical and interview if you want the results to arrive in time otherwise you could have the interview immediately after the medical if you do not mind a delay in processing. As I demand instant gratification this was not an option for me.
I was NOT asked for:
1) Photocopies of the above documents
2) Proof of ongoing relationship
3) or the petition reaffirmation letter Ronnie had signed and sent me as our I129f had expired two weeks prior.
Although an overwhelming amount of people are never asked for these things at London, if it gives you even the slightest peace of mind, take them with you. Just because it is the case for most does not mean it is the case for all as it highly dependent on the IO.
Good luck everyone, may the Llama of happiness forever spit in your direction.