Ian,
I agree that it sounds like it could be a suspension issue.
In addition, have you had the car towed at all lately?
I had my car towed by a flat bed once, and they used my rear control arms as chain anchor points. They bent them both badly, but also linearly, so it was difficult to tell if that was the original design, or they were bent. I actually had to go to the dealer and look at a new one to determine it was bent.
Eitherway, it had the same feeling with any moderate turn felt like the rear end was kicking out.
Take a look.
