OK, you fire engine enthusiasts, add Land Rover registered 107703 to your list.
I think it must have been a prototype, and it was 'registered' with a plate previously issued to (wait for it..... ) a trailer! Not the first time a plate was 'reused' for vehicles under trial, for example, the amphibious Land Rover and the concept demonstrator 1 ton GS truck both used the same reg plate at different times.
No info on chassis or other details. Seen under test at Trial and Proving Wing in the 1960s.
Mike C