I'm pretty sure France and the UK are on very good terms. After all, the French sell the United Kingdom their electricity. So there wouldn't be a way between the two. And even with the UK likely assisting France with Germany, they'd have the troops to spare to defend their North Sea Oil claims from Scandinavea, given that a war with Germany would not be spread over a three different fronts, two of which would need British attention to some degree.

So England would still have a comfortable amount of attention to giving Sweden and Norway attention while giving a few brigades to France to man the border and draw the front in Europe up into an almost First World War status.

And by actually taking action against the UK for an island, you'd be getting wrapped up in a war where you're not going to make your goals.