hi,,my car is a Audi A4 1995 (R) 1800cc 173k on clock

i just went out in my car pulled up and gentlemn tells me i have a leak at the rear of my car.
i get out to investigate and notice a lot of fuel leaking from the rear of my car,around the tank area,but my fuel gauge on the dash remains at same posistion.
so i quickly get home and see that the fuel is still dripping, the underside of my car is soaked with fuel,also for a few months now the smell of fuel circulating inside my car is terrible.
i carnt see under the car properly but looks like its leaking from above the tank,but i really not sure.

any advice what can be wrong,or shall i just throw a match at it