Roger asked "how much rain"? Cats and dogs. July 09 rain was 3x normal in south and 2x normal in north. Western Welsh mountains are much wetter than eastern Wales - more like Scotland or Ireland. We frequently had prolonged torrential driving rain, and the Cambrian Way is primarily in the moors, with no trees or buildings. Quite an experience.
The second half of our trip, Eastern Wales on Offa's Dyke and then on into England, was quite dry and had trees and buildings to boot! We had day-time rain for a total of just a couple hours during the last 3 weeks of the trip -- our reward for the first 2 weeks.
Casey asked about setting up in the rain. We set up in the rain (and wind) for ~10 of our first 15 nights. We didn't carry a footprint, so couldn't do that trick. I think it would be tough for one person to minimize saturation during setup, but with two people it is possible. I can't adequately describe how - practice it at home to figure out a system that will work. We got pretty good at it.
I line my pack with a trash compactor bag. Then, inside and at the bottom of that I put the down double-sleeping-bag and camp-only clothes, in its own plastic bag. I put all the other keep-dry stuff in the outer plastic bag and rubber-band it shut. Then, the rain gear and the food/gear for the day is outside that plastic bag so I can access it during the day.
Jim carries the tent, vertically on one side of his pack. On the other side is a vertical plastic bag with his keep-dry stuff. His rain-gear is on top. So we don't ever need to open our plastic bags until the tent is up and we are inside.
When we get in the tent, every surface is soggy. We keep the dry stuff in the plastic bags until we finish wiping everything down with MSR packtowel - essentially sponge dry the whole system, ourselves and our gear. In that sense it doesn't really matter how much rain gets in during setup, you can sponge dry it before exposing the dry stuff.
I'll close with a plug for walking in Great Britain. The 5-week Wales/England loop was our 6th trip there (3-5 weeks each), and we have enjoyed all of them.