Petrol evaporates! It could be something like the petrol filler neck corroded that's having petrol sloshed when driving, but not dripping when parked.

Worth a look, I may get the opportunity to do that tomorrow, thanks

Is there access to the tank pump under the back seats?

I don't know, but having now had a look at and under the car myself, i'm not sure there is any need!. Frankly i am bemused at the fact that she could see no evidence of a fuel leak, and am quite astonished that the garage she took the car to could find nothing wrong!.

I was at her house this afternoon to clean her windows, and could immediately see a dark patch under the back of the car. Furthermore, when i got down to have a look underneath, it was obvious to me that there is petrol leaking from the seam at the rear of the tank. Goodness knows how the garage could have missed that with the car up on a ramp?.

Not really sure what, if anything, to do about it though. She will get her new car around the 18th of next month, but i have suggested she try and get it sooner. She doesn't use the car very much, but she does use it. And while she doesn't want to be driving about in an unsafe car, she doesn't want to be shelling out for a new tank, especially as the Hyundai dealer is giving her a pittance for it against her new i10.