In reply to climb41:
It's a couple of years since I last did Wilmslow, but I don't think the numbers really slow you down. It can be busy at the start, but as long as you start in the right sort of place for your target time, even going with the flow for the first mile or so should not slow you down much. Given that the first 10k is very slightly down hill, it's worth not going off like a rocket. After the start there is plenty room on the road, but enough people around to work with other people of push on using people ahead as targets.
I remember doing the Fleetwood Half and coming out of the toilet to find the race starting, so beginning dead last, over the first two miles I overtook about 400 people to get into about 20th place, for the rest of the race I was running alone, someone 50 metres ahead and someone 50 metres behind. Big numbers of people can be useful for fast times.
There are about three Lancaster half marathons, using different courses, I've not done any, but I've done a 10 miler and a 20 miler by the same organisers. Both good events, although the 10 miler wasn't on a fast course. The half that follows the cycle way along the Lune will probably be the fastest.