Buying Tyres - National vs. Blackcircle

I have always bought my tyres from National Tyres on the Bath Road in Bristol (close to where I live). However - I thought that I would try an alternative this time - as I need four new tyres for our car. I did the Internet thing for the tyres I wanted - Dunlop SP1s. The price from National was £435.30 fully fitted. That seemed a little steep to me - so I did a search and came up with www.blackcircles.com - who were offering the same four tyres, fully fitted, for £269.24 - that's a difference of £166.06. An added bonus is that Blackcircle also seem to give Tesco Clubcard points on their tyres - so I have gained over a thousand points on this transaction. I nominated a local fitting station to fit the tyres. It should happen next Thursday - so I will report back on the experience.