Come on Joe,
Euros paid into an offshore account! sounds to me as if you knew full well that there was no tax being paid. The problem is, looks like you are about to get caught.
The industry is full of contractors who are paid offshore, all thinking that its OK for the rest of us to pay our dues, but not them.
If you are found out, they will fine you at least 100% fine, on top of any tax etc that is due.
If i were you, i would get an accountant on the job and come clean first.
BALLSOUT.