The following is taken from CAP493, the manual of air traffic services. Section 1, chapter 4.
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, or no delay, when 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
(SERA.11012(a)).
10A.5 At locations where EATs are not issued until the amount of delay reaches a particular
value, controllers must provide a general indication of the delay, based on the best
information available at that time (see ENR 1.9-4).
10A.6 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.7 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, or no delay, when 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.8 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 (SERA.11012(b))).