I'm a student pilot, so take this with the proper skepticism.

I'd expect the following:
1. It's probably airport or city specific, not national law.
2. I would guess it's most likely a noise abatement procedure.
3. As with noise abatement in the US, aircraft and passenger safety
would probably be a legit reason to deviate. I guess it would come
down to the airport administrator as to whether or not they'd want to
make a fuss.
Just my $.02, any thoughts from someone who actually KNOWS?