yes, they do charge £15 a corner to fit your own tyres, which i think is fair enough. i checked the internet prices before i went last time and all things considered i'd be saving less than £10, not to mention having to wait for the tyres. i'd much rather spend the extra and give it to a local business.
tyson fitted the two tires i bought plus he fitted an old tyre i had in the garage for free. performance wanted to charge for fitting my own tire, even though i was giving them over £200 for two brand new ones!