I had a bad experience at Heathrow too – with a company called Heathrow Parking 24 -7.,- I think they are still trading but from different addresses.
My car has cream upholstery and was nearly new – it came back on time and I was met – but the car had a large stain on the rear seat upholstery – I think a combination of chewing gum and oil. Even a professional valeting company failed to remove it and a new seat swab was £400. Every time I sent a letter of complaint to their addresses – including their registered address – it was returned unopened even when sent by registered mail. That is a good way to deal with customer complaints!
Like others report – the car had more miles additional on the clock than I would have expected, the back seat was full of crisp papers and drink cans and the radio was tuned to the Parkistan cricket match!! Never again. I now use the Heathrow Carparks and keep the car keys firmly in my pocket. The service is just as fast – you just need to get the transfer bus. Last time got a really grumpy driver at T4. but the car was safe.