Between the neck of the tank and the filler cap there is usually a rubber coupling between, as you were getting a large amount of vacuum in the tank, this may have disturbed the connections at either end of the coupling, what would happen if this were to be the case, fumes from the tank would seep into the car or when filling, fuel would maybe not directly feed into the tank, spilling some into the car. Not knowing the location of the tank in the Vectra, but some tanks form part of the luggage space floor, and the fuel gauge sender unit is fitted onto the top of the tank, maybe the seal to the sender has been damaged causing fumes to escape into the car from there, or maybe you have a leak in the fuel feed pipe or another leak elsewhere, try to establish where the smell of fuel is at its worse and search that location for a leak first.
