When an airport like Gatwick shuts down it may be that declaring a fuel emergency is a good way to get to the front of the queue and ensure that you are diverted to Luton and not to Prestwick.
Pilots don't declare a fuel emergency unless it's actually an emergency and there would be serious repercussions if one was caught doing it just to queue jump.
@radar are we talking actual emergencies or just a few pan pans?
When an airport like Gatwick shuts down it may be that declaring a fuel emergency is a good way to get to the front of the queue and ensure that you are diverted to Luton and not to Prestwick.