A European patent effectively breaks up into a bundle of separate rights in each country in which it is validated in.
A European patent can be opposed centrally within 9 months of its grant (EPC art 99. If the opposition is successful, the European patent (and the downstream national rights which flow from the European patent) is revoked (EPC art 101). Thus if a European patent is successfully challenged through the opposition procedure, there is nothing left to enforce afterwards.
However, after this 9 month period, the right in any country stands alone. So even if the UK validation of a European patent has been revoked by a UK court, it may still be in force (and ostensibly could be enforced) in Germany and France.
Of course, the argument would be that if a UK court found the claims to be invalid, the French and German courts probably would as well. But until you test it, you never know.
The bright future
In principle, the unitary patent covering all the EU should be available at some point soonish (though exactly when is rather unclear, in view of the Brexit vote). A unitary patent would be revocable in a single procedure at any point during its duration.