this usually happens towards quarter end, you can get some very good discounts as they sell on ~1yr old demo models. You can get around £1/mile discount, so you'd be looking at around £12k discount for a car that's done 12k miles. Saw a couple of these back in June, nearly got one but they go very quickly.
Downside is tot up the approx number of test drives they will have done then think of the condition of the car and how many times it has been floored! Still, I think they're a good buy if you can get them