Mate... There's sommat I've gotta show you.
If you are thinking of doing the London then the Finchley 20 is a really well established race, dating back to 1933.
You get a really good enamelled medal, goody bag, changing/showering facilities, a bar, light refreshments and have the satisfaction of running in the countries oldest race with an outstanding UK record course that has been not broken for 32 years.
If you are preparing for London then you will want to run a race that will test you mentally so that you gain the confidence to feel good about yourself. If you can complete the Finchley 20 you know that you are going to do a good time for London.