Good afternoon, 'Michel'; I am sorry about the predicament in which you now find yourself. Having once broken down in Sweden with my 340 I know well that it is no fun breaking down in a foreign country.
Are you sure that the two events are related. Volvos are robust cars and would normally not be adversely affected by driving through surface water - I'm assuming that it wasn't a flood of Biblical proportions!
The fact that the car drove normally to the fuel station would lend weight to that, I would think. I think the WNS is more likely to be fuel related. No disrespect, but might you have accidentally mis-fueled? Alternatively, have you inadvertently filled up with some bad fuel? If the garage storage tanks were very low and / or they had just had a delivery it is possible that you may have taken sediment or water on board with your fuel.
How low was your own tank when you refueled? How much fuel did you take on board? You've carried out checks and ruled out the most common causes, so I would be inclined to look elsewhere, especially if your car normally runs well.
I'm afraid that not living in Scotland I can't personally recommend a garage, but I understand that Volvomax are well thought of among forum members.
I hope that you are able to quickly and successfully resolve your problem and can continue with your journey.
Regards, John.
Edit: Posted before I read 'duke1's post above. We were clearly thinking along the same lines ...
J.