I've just gone through this process myself for the FLR(M) just yesterday at the Birmingham PEO. Generally, the way it's done is, you come in, they issue a ticket to you with a number on it as well as what I believe is a home office reference number (attached is a picture of mine). You then are called to one of the counters (1-5, typically). You speak to a worker there who asks for passports of the applicants (including dependents) and the passport of the spouse. Then they ask for the pictures that were required and the marriage certificate. Oddly enough, the application asked for additional documents (birth certificates of applicants, previous marriage docs and proof of it's legal dissolution, if any, and financial information). However, when we were there, they did not ask for any of this, and it was explained that all of that would have been verified during the consideration of the entry clearance visa.
After this, they send you to counter 6 (which is a cashier) where you make your payment. You then go back to the waiting area and get called to either counter 9 or 10, and biometrics are done. From there, your application is put into a consideration phase, and usually between 20 minutes to an hour, you are called back to one of the counters 1-5 and told of your result (you know before you leave if you got approved or not) and then it's explained that you'll receive an ICFN (identity card for foreign nationals) and that this will be in the mail and should take no more than a week to come in. They also give you a letter which formally explains your rights from this point and also gives details about the identity card as well. From this point, you're able to leave.
Mine was just approved yesterday (and took about an hour to be considered and approved) and now I'm just waiting on the card to come in.
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