Phone your usual plumber and tell him what you have here, sound knowledgeable and say the diaphragm needs changing in the diverter valve. That way he can come armed with the right part (good engineer will always carry stock in the van), job done from 2 mins to 2hrs.
£10/£20 for the diaphragm, say £30hr.
£10/£20 for the diaphragm, say £30hr.