Water doesn't stop flowing when shower is switched off.
Andy Stagg replied to my request on myworkman.co.uk within 24 hours, with an estimate which he refined as I gave him more information about the exact shower that needed to be replaced. On a Friday afternoon he offered to call at 9 a.m. on Tuesday, and he arrived right on time. The work was done exactly as planned, and the cost was what Andy had estimated. I am posting this review a week later, during which the shower has been used about 15 times and performs very well indeed. Great work!