Thank you for all your advice. As I said at the start, I was out of date with CofA stuff as I had exclusively dealt with permit over the past 2-3 years. I guess I was kind of hoping that things had changed a bit and the rules relaxed somewhat but I guess nothing has changed.
For me, I certainly could not take the risks on the sort of costs I am hearing. On another forum, £700 to supply and change a seat belt. On permit, about £40 for a very high quality seatbelt and 3 nuts and bolts to undo and do up and 15 minutes of my time and a descriptive entry on the logbook with receipts.
Surely there is going to come a time when some of the older aircraft (that are quite serviceable) are going to be cost prohibitive to own even for a group in some circumstances. The CAA should really start thinking about a category for the purely leisure flyer that just really want's to potter around in a well built, old but very serviceable aircraft. It seems to be an all or nothing situation at the moment for CofA.
I would quite happily own a C172 without being able to fly night or IMC. Only flying it in excellent weather conditions and keep it serviced to probably a higher standard than I am required to at present. I have just overhauled the engine on my own aircraft. It didn't really need it and was well within the manufacturers specifications but I had 2 compressions that were lower than the others and I wanted to bring the engine up to the latest specification. Again, I had no legal requirement to do this. This would have been a no go in a CofA aircraft unless I had excess cash that I didn't know what to do with.