Like Cows getting bigger, I have refused a clearance below safety altitude and stayed on the ground until it was changed. I also agree with Journey Man that each sovereign state 'owns' its own airspace and can decided the rules which govern it - therefore, it is our business as pilots to know these rules.
However, I have long been an advocate of a common transition altitude across the whole of Europe, either 18,000ft, as in the States, or 15,000ft (it doesn't really matter which) as a means of reducing yet one more source of error.