Update
Plumber came to look at the job today. He is a lot bigger and somewhat younger than me and after about 5 minutes wrestling with it was in the bathroom wash hand basin draining. :-)
Now I can get it on the bench, I can see what the problem is. One of the brushes is sparking excessively, but can I find out how the brush comes out? Can I hell.
New shower is being fitted Sunday morning.
Dave