I believe Schiller is correct. The holes in the harness were quite large, as was the central pin (and, I'd assume, with thick gauntlets on, was not particularly easy to undo, particularly in 'less than ideal conditions'). And then there was the headset lead, which back then, was large, and separate to the oxy mask lead and usually behind your head.
In having the Sutton harness, the Brits were ahead of some of their allies. I was surprised to find some of the US types of that vintage didn't have a shoulder harness, but just a lap strap, with not very reassuring double webbing 'poke in' securing points. This lack of a shoulder harness could lead to terrible face/head injuries on gunsights in forced landings in single engine types.