I do this run regularly in helicopters, last week it was from Blackbush. I usually route MID-SITET-LHO-DCT. If you go via the reporting point at SITET ATC on both sides know where you are (roughly) should the horses all escape from your motor, Deauville ATC are first class and the airfield is certainly very pleasant, as someone else said, file your return flight plan before you leave the UK. The ramp checks appear to be aimed more at N reg aircraft these days, certainly I've visited Deauville at least once a month for the last 5 years and never been stopped once.
FF