Have a look at Performers Theatre School in Liverpool-they have a website with lots of info. The younger children get quite a few opportunities to audition for touring productions at the Liverpool Empire.
Not a big expert on these, but I do know of this one in Manchester as my niece has been to summer schools there and had a great time http://www.footlightstheatre.co.uk/
I know the people who run the Salford & Didsbury Stagecoach schools. They have a very good reputation and one of dd's dance teachers works there. They have some really good teachers by all accounts.