I am rather dubious of the claim in this article that all but one of the trains will be longer than 12 carriages. Is that even possible at Brighton?
https://www.theargus.co.uk/news/17781795.train-stations-will-closed-brighton-pride-weekend/
Trains will run through the night right into the Sunday morning timetable, according to National Rail Enquiries, and all except one train will be longer than normal full-length 12 carriage services.
https://www.theargus.co.uk/news/17781795.train-stations-will-closed-brighton-pride-weekend/