Interconti... I said the emergency category is decided by ATC, which it is.
The pilot can declare an "emergency" but what happens thereafter is decided by ATC based upon information from the pilot. There are also situations when ATC determines that an emergency exists before the pilot knows about it - typically burst tyres. These can be seen from tne tower and the fire service will be on its way before the pilot may be fully aware.
All the best..