Not sure if this has previously been posted here, but for anyone looking for plumbers, roofers, electricians, decorators, gas fitters & gardeners can always refer to Southwark's trading standard's service. They produce a list of traders who have undergone a strict vetting procedure and who meet certain minimum standards as per Southwark's code of practice.
I recently used it to find a plumber. My shower's thermostat had broken and the company that fitted it 6 years ago no longer do bathrooms. I was unable to find the brand of shower and so most plumbers were indicating that the only thing to do was to replace the whole shower unit and potentially redecorate the whole bathroom (as I doubt I'd have been able to find the same mosaic tiles either). I called Blue Plumbing in Waterloo (who had also had a recommendation on this site) and they had no problem in recognising the make of shower and ordering a replacement part, saving me loads of aggro and £££££.