Smell Of Fuel From Engine

[Funky_Monkey]

Hey guys,

So I've recently noticed a smell of fuel getting into my cabin whilst sat idle at traffic lights ect. had a quick inspection whilst it was quiet at work this afternoon and cant see any of the injectors leaking and the exhaust isn't blowing. The strange thing is the smell seems to be coming from just behind the cambelt (see picture). The smell disappears as soon as you turn the engine off and comes back as soon as the engine starts up.

I've had no problems with my MPG and everything seems to be running fine just can't figure out what could be causing the smell. Just hoping someone might be able to help me out.

Thanks in advance :)