Fuel leaks when filling

My 02 reg Renault Kangoo 1.4 petrol has been modified for wheelchair access via lifting rear door. The fuel pipes have been extended but are supposed to be similar to original. It used to be fine, but now, when I add fuel, (a) the filling process is slow, nozzle clicks if handle is squeezed fully (b) lots of fuel spills onto floor under car. Once I leave the forecourt, the dripping stops. Whilst filling, it's more of an open tap than a slow drip, the puddle of spilled fuel is probably 5 litres from a 25 litre top-up. As well as wasting money this is dangerous. I cannot see any obvious cracks, splits, or source of the spill. Please help before I cause a fire.