Impossible to say without seeing the car in the metal. However, given the reported stuttering, I'd be very concerned that the petrol has caused friction and then damage within the fuel lines, pump(s) and/or injectors. The car will need to be inspected by a mechanic and the fuel systems drained and flushed. At best, it'll be a couple of hundred pounds. At worst, a few thousand. Do not drive it, under any circumstances.