If you have an order placed prior to the last price increase, you already have a notional price 'benefit' of about £1,500 over the current price. Add in another price increase of at least £1,000 (Lexus would not be daft enough to price the car with metallic just over the threshold), then you have a 'benefit' of around £2,500 compared to the market prices at the time you would be making the decision to cancel. Assuming Lexus prices maintain a similar competitive level to where they are now, then if you cancelled your order and went for another make you would lose that £2,500 'benefit' because you did not want to pay the extra VED of about £1,400 over years 2 to 5 of ownership.
I'm not sure I'd follow that route.