I agree with Severn Trent. Since we don't know what brand of machine will be fitted (and assuming most people fitting the machines won't know about check valves or the Water Regulations), I prefer to err on the safer side too.
Interestingly, John Lewis fitted a washing machine in my house while I was abroad. The machine does not incorporate backflow protection, and the (German) manufacturer did provide a screw-on check valve the installers could have used when connecting to the appliance valve. John Lewis did not fit the supplied check valve, yet I fail to see how the installers could possibly have known that I had fitted one to the pipework upstream of the appliance valve, given that the pipework is entirely hidden behind a cupboard. In theory, this was a professional installation.
