Hi All,
Thought those of you who may have been interested in this subject, should have an update.
I never did find out why the suite changed colour, though I'm almost certain it was due to an unstable dye in the fabric being removed, when cleaned. All the de-brown treatments made no difference, and this to me is why I can rule out cellulosic browning.
Anyway, finally gave in - I put it in the hands of my insurance company and they are going to replace it with a new, like for like. My excess is £250, so not exactly jumping through hoops. My first claim for anything of this nature since I started nearly 25 ago. Could have cost a lot more had I not been insured - Get the message.
Dave.