The standard seat harness during WW2 was the Sutton Harness, a pre-war design made of cotton canvas webbing. This was modified and up-dated in the late war period, from about late 1944, in fighter aircraft at least, being a similar design, but made from a more modern fabric, and with the addition of 'slider' type adjusters, and a modified rekease catch. Most aircraft used this harness, although certain types might just have a lap belt for, for example, a bomber navigator or radio operator.
There was no standardisation, as such, on the type of seats used, with each manufacturer tending to fit their own design for a particular aircraft type. To be certain, the only way to identify a particular seat and harness combination, would be to state the particular aircraft and Mark number.
Additionally, many American aircraft used by the RAF and FAA were fitted with British harnesses, safety equipment and radios etc, after import into the UK, but therw were exceptions. For example, the P-51 Mustang retained the American seat harness, but had a British radio and magnetic compass, to compliment the US gyro compass.