I suppose the international nature of the dispute will be a problem.
The article claims Coughlan broke his contract with MWR in April, and then signed with Williams in June. On the face of it, Williams seems to be in the clear. Certainly a British Company isn't required to ferret out if someone has a pre-existing contract with an American company.
Now, some industries include 'anti-tampering' languages in their contracts, if that's the case, Williams might have offered Coughlan the job before he quit, but once again, that's going to be tough to determine, and again, a NASCAR contract might stand up to EU regulations anyway.
At the end of the day, do you really want someone on your team who doesn't want to be there? Can MWR get good talent if the team won't let them explore other opportunities?