Hey guys this is my speciality. Product Placement in this country is still against the OFCOM code (with the exception of American imported television). It's not product placement if the production company receives no money for it. If they get loaned cars for the program for free, that's okay. However, if one product is shown too much, it can breach the "Undue Prominence" rule. This can be measured over the course of a series, so if over the series they show a lot of different cars, it's fine.
The use of the cars has to be editorially justified, i.e. fairly natural in the program. I.e. you can't have the car company saying right, I'll lend you these cars, but I want the first shot to be a close up of the badge zooming out to a leggy blonde stepping out of the car in a very short skirt".
As much as I wouldn't mind to see that sort of thing, it's not acceptable