I checked my tyres (sorry Tires!) and noted the stamped manufacture date of 08/04, meaning they are more than 11 years old.
I found the original receipt (kept by previous owner) from the Tire Shop (26 October 2004) that fitted them that also indicated mileage of 127,633. My car now 131,200; meaning although they are 11 years old they have only travelled 3,600 miles since fitted.
After reading all the comments below I decided to change them and at the same time change to whitewalls.
After much research there seem to be only 2 or 3 brands available. I went with Sumitomo 195/75 a mid priced tyre (from a very small selection!)
After fitting today I went for a drive - wow - the difference in the ride quality is amazing, no screeching when cornering with some power and an overall much smoother ride, no jarring that seemed to occur with the old set.
I discussed tire life with the owner of the tire shop, with more than 30 years in the business. He was absolutely adamant that tires have a 6 -7 year life and that all sorts of degeneration starts after 6 years.
He also said that, assuming mileage is not a factor, for older cars like ours he would even consider changing after 5 years because as the suspension systems on ours are not as sophisticated as modern cars, the tires may be a relatively more important component of the road adhesion and control processes than more modern cars.
Also - I like the change to whitewall.