Only obligation re ICAO is to notify if we differ.
I have always said that resources should be allocated to a Unicom and a Tower before resources are allocated to RFFS. Just commonsense that you attempt to prevent the accident first.
Also the RFFS should be run by the airport owner- not from a giant in -efficient government monopoly. Then the staff can be multi skilled and we will get twice as many RFFS for the same money. Therefore lots more safety.
It was coalition policy . But under Mr Truss nothing happens.