Hi OP, my son has autism too. Here are some things I've found:-
Merlin attractions (legoland, sealife, alton towers, chessington, cadbury word, bear grylls, blackpool tower, bpool circus). You need to get a nimbus access card which shows what accommodations the children require and you'll need evidence to prove it. They offer either one or two free carers depending on what is shown to be needed and a ride access pass to access rides easier.
ATG for theatre productions. They do relaxed shows which are great and also offer free carers tickets with nimbus card.
Arena's (think disney on ice, mega trucks, concerts etc) nimbus card again.
Paultons Park I think from memory last year changed over to nimbus too.
Cinema, you can get a cea card for free entry. They do autism screenings too. See dimensions website. Cea card cost £6.
Have a look on the websites of anywhere you fancy. Lots of places offer free carers with proof or queue bypass if needed.
Museums do autism friendly sessions too.