To be honest, it's not the £20k that needs thinking about, it's the running costs and reliability. I mean it's all well and good having a TVR, but can you put a weeks worth of shopping from Tesco in there? And go through the drive through for a big mac? Lol!
New cars, you're not going to get much for your £20k. A decent spec Nissan Qashqai costs more than that!
You could get a year old S3 or a half decent BMW. Golf GTi, Scirrocco, so your running costs will be similar to the Clio's.