Hi Mike,
The theme is Best of British to coincide with the jubilee.
I'm afraid a Delorean is as British as a Nissan built in Sunderland, a Toyota built in Derby or a Honda built in Swindon.
I doubt they'd let you into the themed car area. Even if you blag your way in to some dumb marshall, you'll get a few ugly comments from the die hard enthusiasts.
Its a day for Jaguar, Morgan, Rolls, Bentley, Aston, Alvis, Morris, Triumph, Austin etc NOT an American Car, from an American Company that was set up by an American, who's Company was registered in New York . There are more appropriate Breakfast Club themed days to take a Delorean to.
I'll definately be there, I go every month, but not in my D.
Good luck if you make it to the event, but don't be dissapointed if they send you to the public non themed car park.