I didn't have my pre-op appointment in London, so can't help with the logistics, but I can tell you how the appointment went.
I'd strongly recommend writing down any questions you have in advance and take them with you. Even if you just put them in your phone.
My pre-op appointments were two separate ordeals. The first, I met with a nurse and filled out their paperwork. You'll probably need to have information about medications you're on and if you have any health conditions they'd need to know about. They discussed which procedures were options, and asked about preferences I had. The surgeon came in and took a look at my chest, made her recommendations, asked if there was anything I specifically wanted or didn't want. And that was that.
Three weeks before surgery, I went back in and talked with just the nurse. She gave me paperwork for pre-op bloodwork, prescriptions for pain pills/anti-nausea pills/anti-anxiety pills/sleeping pills, and went over the list of things I wasn't allowed to consume in the weeks leading up to surgery. It was pretty quick.
It's nothing to get nervous about. I'd recommend asking about timelines for returning to work, resuming exercise, potential revisions, etc.