Try AutoTrader. I can find a copy of an AutoTrader at my local WHSmith and Tesco, but I couldnt find Loot. Maybe I didnt look hard enough.
The Autotrader is placed much closer to mags like Autocar and AutoExpress anyway. I think there is a higher chance for the AutoTrader being picked up than the Loot.
Anyway, would you tell me what car you are selling? Is it ok to tell me?
I do a little bit of car trading in my spare time, at the moment I have a Volvo in Loot, but not getting many calls. My brother does it full time and always uses Autotrader, but he doesn't live in London.