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I have recently been getting the occasional smell of petrol inside my car, when putting the back seats down i found a small pool of petrol under the rear seat behind the driver. It seems to be coming out of the black circular thing but i have no idea what it actually is

Can anyone identify this for me? Also has anyone had the same problem?

I have a P reg 1.4cl (if thats makes a difference)

if I was you mate I wouldnt mess around I'd get it straight to a garage to find out what the cause is. but Im afraid I have no idea what is causing it.