A gas turbine engine comprising: a main compressor section and a turbine section, said turbine section having a first turbine blade and vane and a downstream turbine component; a first tap configured to tap air from said main compressor section at a location upstream of a most downstream location of the main compressor section, and said tap connected to a heat exchanger, the heat exchanger connected to a cooling compressor, and the cooling compressor connected to said downstream turbine component; a second tap configured to tap air from a location in said main compressor section, and said second tap connected through a check valve to a line leading to said downstream turbine component; and a control for operating said cooling compressor such that when said cooling compressor is operating, air downstream of said cooling compressor is at a pressure higher than the pressure of said second tap, characterised by said control being operational to selectively drive said cooling compressor at high power operations of the gas turbine engine, and to stop operation of said cooling compressor at lower power operations of the gas turbine engine, such that air is delivered through said cooling compressor to said downstream turbine component at the high power operations, and air is delivered from said second tap at least some time when said cooling compressor is not operational, wherein a first controlled valve is provided intermediate said cooling compressor and said downstream turbine component and may be closed to block flow downstream of the cooling compressor by said control, wherein a second controlled valve is positioned between said second tap and said downstream turbine component, with said second controllable valve also being controlled by said control to selectively block flow to the downstream turbine component, and wherein at high power operation said second controllable valve on said second tap is closed and said cooling compressor is operated and said first controllable valve is open such that high pressure air from the cooling compressor is delivered to said downstream turbine component. a main compressor section and a turbine section, said turbine section having a first turbine blade and vane and a downstream turbine component; a first tap configured to tap air from said main compressor section at a location upstream of a most downstream location of the main compressor section, and said tap connected to a heat exchanger, the heat exchanger connected to a cooling compressor, and the cooling compressor connected to said downstream turbine component; a second tap configured to tap air from a location in said main compressor section, and said second tap connected through a check valve to a line leading to said downstream turbine component; and a control for operating said cooling compressor such that when said cooling compressor is operating, air downstream of said cooling compressor is at a pressure higher than the pressure of said second tap, characterised by said control being operational to selectively drive said cooling compressor at high power operations of the gas turbine engine, and to stop operation of said cooling compressor at lower power operations of the gas turbine engine, such that air is delivered through said cooling compressor to said downstream turbine component at the high power operations, and air is delivered from said second tap at least some time when said cooling compressor is not operational, wherein a first controlled valve is provided intermediate said cooling compressor and said downstream turbine component and may be closed to block flow downstream of the cooling compressor by said control, wherein a second controlled valve is positioned between said second tap and said downstream turbine component, with said second controllable valve also being controlled by said control to selectively block flow to the downstream turbine component, and wherein at high power operation said second controllable valve on said second tap is closed and said cooling compressor is operated and said first controllable valve is open such that high pressure air from the cooling compressor is delivered to said downstream turbine component.