A fuel supply system for delivering fuel to a first use and to a second use on a gas turbine engine comprising: a first pump for delivering fuel to the first use on the gas turbine engine, wherein said first use is in a combustion chamber; a second pump for delivering fuel to the second use on the gas turbine engine, wherein said second use is as a hydraulic fluid for at least one accessory actuator; and a valve including a valve housing, said valve housing being provided with a port to communicate said first pump to said first use, with a port to communicate said first pump to said second use, and with a port to communicate said second pump to the first use, characterised in that said valve has a first position allowing flow from said first pump to be delivered to the first use, but also routing some flow from said first pump to supplement fuel flow from said second pump until a pressure downstream of said second pump increases to a pressure at which the valve moves to a second position, and said valve in said second position then allowing flow from said second pump to flow to the first use to supplement the flow from said first pump, wherein said valve includes a bias force which biases a valve spool in opposition to the pressure downstream of said second pump, and wherein said valve spool when positioned in said first position allows flow from said first pump to supplement flow from said second pump to the second use, and also allows flow from said first pump to be delivered to the first use, and blocks flow from said second pump from passing to the first use until the pressure downstream of said second pump increases enough to overcome the bias force on said valve spool. a first pump for delivering fuel to the first use on the gas turbine engine, wherein said first use is in a combustion chamber; a second pump for delivering fuel to the second use on the gas turbine engine, wherein said second use is as a hydraulic fluid for at least one accessory actuator; and a valve including a valve housing, said valve housing being provided with a port to communicate said first pump to said first use, with a port to communicate said first pump to said second use, and with a port to communicate said second pump to the first use, characterised in that said valve has a first position allowing flow from said first pump to be delivered to the first use, but also routing some flow from said first pump to supplement fuel flow from said second pump until a pressure downstream of said second pump increases to a pressure at which the valve moves to a second position, and said valve in said second position then allowing flow from said second pump to flow to the first use to supplement the flow from said first pump, wherein said valve includes a bias force which biases a valve spool in opposition to the pressure downstream of said second pump, and wherein said valve spool when positioned in said first position allows flow from said first pump to supplement flow from said second pump to the second use, and also allows flow from said first pump to be delivered to the first use, and blocks flow from said second pump from passing to the first use until the pressure downstream of said second pump increases enough to overcome the bias force on said valve spool.