Bloody plastic tailed fill valves are nearly always terribly brittle plastic.
I use the brass tailed valves, - even fitting one on a brand new toilet I was installing in a flat recently. The thought of the plastic tailed valve supplied with the toilet cracking and flooding the flat and others below put me off fitting it.
Those Hepworth rubber washers can be bought in 22mm also. They are obviously supposed to do hot pipework, so should be good.
Never use tap connectors with any flat washers on valves that have a taper designed for an olive though, - too sharp an edge. Brass ballvalves seem to vary, - some are flat ended tails, some are tapered. I carry spare brass tails to use for nut and olive connection, which I prefer.