Having had a good deal of annoyance with the typical appliance water-supply valve, including one where the plastic handle broke and cut my thumb, I decided to use something a bit more solid. The crucial part is the ¾″ to 15mm male coupler; I used Screwfix part number 82086. The valve is a 15mm Pegler ball-valve, though one could use a better valve if one felt the need.
The above image is the one I used for a dishwasher. I used a similar arrangement for a washing machine. Aside from the obvious advantage of being able to use a more reliable type of valve with a more convenient handle, the pipe clips either side of the valve reduce the force applied to pipe joints when operating the valve.