There's the Worthing twenty - not sure what date it is, it was three weeks before the FLM this year which some would consider a little close. I had a bad run but still enjoyed it enormously, in spite of being caught in the bushes having a leak when the starting pistol went!
There used to be a 25k run around Mitcham, but I think that's stopped now, and there's the Kingston 16 mile in the next few weeks. I'm sure there are plenty of others around the country too - these are just races I've done in the past.
Iain