Lifesavers
Shower Doctor's service was first class and the connectors are of high quality.
The original problem was that because the elbows on the supply pipes were set a little too far back in the wall, the doglegs couldn't be wound all the way in. They then turned when tightening the manifold resulting in a wonky bar mixer and minor leakage from behind the showerwall panel no matter how much PTFE tape was used. I must have at least 10 attempts and I also tried True Blue sealing compound which was not fit for the purpose.
The straight fittings were way too long so needed careful cutting down with a hacksaw (take care when winding them in and out as I sliced my hand on the threads).
Thankfully the plumber had set the elbows at the correct centres for the shower and all is now fine.