Sorry - not a very imaginative reply, but here's a copy and paste from CAP 493
10A. Minimum Fuel and Fuel Shortage
10A.1 Once in possession of the estimated delay for an approach a pilot will determine whether
or not he can continue to the aerodrome or divert to a suitable alternative aerodrome.
10A.2 A pilot's declaration of "MINIMUM FUEL" indicates that no further fuel diversion options
are available where the aircraft is committed to land at the pilot’s nominated aerodrome of
landing with not less than 'final reserve fuel'. However, “MINIMUM FUEL” RTF
phraseology is not universally used by every aircraft operator and pilot.
CAP 493
2 April 2015 Section 1: Chapter 4: Control of Traffic - Page 7
Note: Final reserve fuel is typically fuel for 30 minutes of flight for turbine powered aircraft or 45
minutes for piston powered aircraft. (EASA-OPS)
10A.3 Controllers are not required to provide priority to pilots of aircraft that have declared
"MINIMUM FUEL" or that have indicated that they are becoming short of fuel.
10A.4 Controllers shall respond to a pilot's declaration of “MINIMUM FUEL” by confirming the
estimated delay he can expect to receive expressed in minutes if the pilot is en-route to, is
joining, or is established in an airborne hold; or by expressing the remaining track mileage
from touchdown if the aircraft is being vectored to an approach.
10A.5 Once in possession of either the estimated delay or remaining track mileage, the pilot will
determine whether or not he can continue to the aerodrome with or without declaring a
fuel emergency. Controllers shall keep pilots informed of any increase in delay or
increase in track mileage after the pilot's initial declaration of "MINIMUM FUEL" following
which the controller can expect the pilot to declare an emergency.
10A.6 Controllers shall respond to a pilot who has indicated that he is becoming short of fuel but
has not declared "MINIMUM FUEL", by confirming the estimated delay he can expect to
receive expressed in minutes if the pilot is en-route to, is joining, or is established in an
airborne hold; or by expressing the remaining track mileage from touchdown if the aircraft
is being vectored to an approach; then ask the pilot if he wishes to declare an emergency.
10A.7 Pilots declaring an emergency should use the following RTF phraseology "MAYDAY,
MAYDAY, MAYDAY" or “MAYDAY, MAYDAY, MAYDAY FUEL” and controllers shall
provide such aircraft with flight priority category A (ICAO Annex 6).