I find National Tyres to be good on service. Local branch seem to know what they are doing rather than some of the back street boys. However try www.tyre-shopper.co.uk. Choose your tyres and pay online. You pick a convenient local fitting centre and book the appointment when you buy and just turn up and have them fitted. Best part is that the fitting centres are all National Tyres! Prices can be anything up to 20% cheaper than buying direct.
Current price for 4 x Yoko at National £206.86, Tyre Shopper £184.40. Both prices all inclusive.