Oh dear - What's the issue with the shower valve?
So, let's say I kick up a fuss and refuse to pay what he's asking or only pay part of what he's asking... where do I stand practically/legally? In other words, could he try to take action against me to force me to pay? He just doesn't seem to recognise the issues I've raised and thinks everything he's done is fine, so I can tell he wouldn't take kindly to me deciding to deduct anything.
But if I do, how much should I deduct for him not having disposed of the waste (currently heaped up in front garden)? How much do trade customers get charged to dispose of a bath/toilet/sink and a lot of tiles and other rubble?
He could take you to Small Claims Court for any amount extra he thinks he is due but you could fight it or also claim of him.
He would have to prove his work was satisfactory etc, likewise you would have to prove the work was badly done and therefore unacceptable. A qualified plumbers report on the work would be enough evidence for you to take to court to counter your first plumber.
I would take plenty of photos of all the work,the rubble, etc, left not taken away, plus stage by stage removal of faults, like shower tray base.
Manufacturers instructions, building regs for evidence and any quotes your plumber gave you. Judges love plenty of evidence.
I don't think you will have a problem with the plumber as he will know he is in the wrong, but best you gather evidence now and retain it.
Keep any communications - letter, emails, texts, etc, polite and reasonable, as you also need those as proof of your objections, so have copies.
My take on all this is your plumber probably deserves to be paid for any labour done correctly, - so whatever cost for removing old bathroom suite, plus some money for basic labour and not too much extra. You really need what you were going to pay him, to be paid to another plumber