This is interesting. I also had thought that the sensible thing to do would be to go to the UK on a visit and find a flat, then go back home and do all the moving stuff (packing, shipping things off, getting out of the apt) and then go over for good. I thought this for a few reasons: (1) holiday accomodations (hotel, serviced flat, etc) are so much more expensive than regular long-lease flats that my plan would be cheaper even taking into consideration the extra flight, (2) visa applications ask where you are going to live in the UK and I thought a holiday flat would not do, and (3) we'd have an actual place to ship all of our belongings to!
So those aren't good reasons? If we did go for a holiday flat plan first, how long would be a sensible time to reserve it--i.e., how long might it take to find a permanent flat? Two weeks? A month? I guess we could ship all of our stuff to the holiday flat, though that does mean we'd have to move it once we got a place. But we're not shipping much, so I guess we could handle that.
As background, I am the UK citizen (but by decent and live in the US) and my gf will apply for an unmarried partner visa (we will have lived together for 4.5 years by then, so I see no problems with that). We will be moving over at the same time. Most likely, neither of us will have a job (I will look before the move, but I don't expect much response, based on past experience) and we will have money saved up to support us for about 6 months over there while we job hunt.