. . it is a 89 model,I shold be able to get it for 7000£ with my car. What are they like & should I do it,I do 300 to 500 miles a week in my eight it has 115000 on my eight now?
My feeling, and that's all it is, is, "Don't do it."
I purchased a 1979 Silver Wraith II with less than 27K on it in 2012 and am still working to get it roadworthy. Think about it, a 1989 car with 30K miles on it has moved less than 1200 miles per year. That puts it in the same category as my SW-II: barely rolling sculpture. This is never good for any mechanical device. Most of these cars do not die from wearing out but from the direct results of lack of use. In a more complex car equipped with a turbocharger I'd be quite hesitant. Low mileage like this is, in my eyes, a detriment, not an asset.
However, if you know that you're likely getting yourself into a "revival from the dead" situation, and can accept that you're not going to have a reliable driver until you've owned it for a while and worked out the kinks, you could certainly move forward.
A Bentley Eight with 115K on the clock is a mere babe in the woods. I'd stick with the "devil that know" rather than going for the one you don't.
If you decide you want to purchase the car be certain to spend the money for a comprehensive pre-purchase inspection by a mechanic intimately familiar with this particular model. It is money very well spent if for no other reason than assembling a "to do" list.