Hi Xavier - I have same year car, same spec except I also have sunroof and it is Cadoxton Slate (grey) - otherwise exactly the same with 3.5k more on the clock. I've had it 3 years and still love the Lexus refinement.
Pricewise, it is at the upper end of the dealer retail price (£10,995 - £11,995), so maybe some room to haggle a little. I'd be impressed with the low mileage but a little concerned with the towbar, who knows what it's been pulling along. Having said that it has full Lexus service history and the engine is pretty much bulletproof if serviced at the recommended intervals. It's a buyers market now so have a good look around for similar cars elsewhere and as Normski says, offer less and be prepared to walk away, there's a good to great chance they'll be calling you to accept your (reasonable) offer within 24hrs.