In reply to brokenbanjo: Had a very similar experience with the one we were "upgraded"(wow, thanks Hertz) to at Stansted. No power whatsoever, especially up long drags, similarly embarassing when you can't get past a large flat-bed lorry.
The layout was weird too, especially the centre console. My wife and I both agreed that it was truly awful. I've had loads of hire cars, and this was the worst, even more so than the battered Clio we once rented from Alicante, or the completely shagged A-class Merc in central Paris from Easy-rent-a-flight-and-car-and-hotel.com!