Lavenham (hope that is spelt correctly!) It is navy with fluorescent trim, is waterproof but has fleecy/wool underneath so is warm too. Most importantly to me it goes on over the saddle if that makes sense...it covers the quarters but goes under the saddle flap and secures over the withers (I don't like the ones that go under your saddle but that's just my preference). If you want and it's not windy you can actually undo it and put it over your legs when you are on board to keep them dry if it is torrential.
Someone on here recommended the Mark Todd fluorescent one, and I used it for the first time yesterday in heavy rain and gales and it didn't move an inch, and was very waterproof. Brilliant!!