I agree; we do the same - drive to the airport, take out the car seat, put it into a bag and check it in.

My only concern after reading this long thread on the BAEC forum is whether the car seat will be counted as one of our bags if other airlines go to the 2 bags, 23kg limit that BA are introducing.

To answer Swiss Tony's question in this thread, I believe that Volvos (V70?) have built in child seats in some models. I'm not sure if it is a standard fitment or an optional extra but I read somewhere that some rental companies have Volvos with this feature. I usually use Hertz so it was probably them that I was reading about. I can't remember where or when I read about the Volvo car seats though so this info may be years out of date...