Boardman 8.9e Hyb Problem

[dodger1]

Hi. I've had this bike for about a year now, after some invaluable advice, especially Cugel.
It's a great bike but there has always been an issue with the minimalistic control button on the handlebars.
It's now very temperamental about changing between modes and today wouldn't operate other than in lowest (green light) mode.
Anyone else found this, or any suggestions about it??