Have a look at the Charcoal Cannister.
On the top there is a pipe that runs to just below the coolant bottle. Check this pipe. I used to get that and found that i had a snapped pipe. I also fixed someone elses car who had this recently (although his was a loose fitting one)
I haven't got ETKA handy till later but i will post up the part no.s for the pipe on it's own and the charcoal cannister complete.
The pipe is about £9 from a dealer and the Cannister complete (including the pipe) is about £90
I will post pics up of the pipe from mine later. But that would be the first place i would check. I've seen a few cars with this and it's always been that pipe.
Tell your mate not to brim the tank when refuelling as i think this is what causes the problem. I have stopped Brimming mine and the problem has not re-occured in the last 10k miles (this is just my opinion as to the cause but was suggested to me by my local dealer)
In either case it doesn't require a trip to the dealers to fix. Anyone with a basic understanding of using a screwdriver/spanner can do it. The pipe is literally a 5 sec swap