Structurally-critical components operating at high temperatures and in high pressure gaseous environments can display cracking behaviours that are not replicated using conventional mechanical testing methods which simulate the temperature but not the gas environment. Such behaviour appears to have been observed in both UK nuclear power stations and industrial gas turbines. This raises questions about using existing laboratory data for estimating the lifetime of in-service components. There is a need to confirm whether gas environment has a significant impact and develop a mechanical testing capability that better simulates these high temperature and pressure gaseous environments. This would provide a capability which is believed not to exist at any other facility world-wide, and is certainly not readily available. This project brings together a consortium of organisations to address this problem, from a user perspective and also in the provision of testing capability, with suitable instrumentation. Detailed microscopy will be undertaken to demonstrate the differences in behaviour seen between cracked ex-service components and cracks produced under current laboratory conditions. Alongside this, a facility will be designed and built to enable fatigue initiation, and fatigue and creep crack growth tests to be conducted in relevant environments for nuclear power stations and gas turbines. Initial trials in the pressurised gas facility will be undertaken to demonstrate its operation and provide an opportunity to determine the reproduction of ex-service behaviour.