Environment too, not just economy
>>> And it has automatic stop start ... This is all done in the name of fuel economy ... It's a £200 option, so would need to save a lot on petrol-guzzling to justify itself.
It's done as much for people walking past the car as much as those paying for the fuel. Nobody likes breathing in exhaust gases.
>>> it has the highest output per cubic centimetre of any car in current production.
Don't think that's right. Some of the exotica has it firmly beaten (e.g. McLaren P1 at 191 bhp/litre, although strictly speaking not in production any more), and for more mainstream metal, the Mercedes-Benz A45 AMG and Audi S3 are ahead (181bhp/litre and 148bhp/litre).