Well, it's up and running and I am delighted. Perhaps a second transformer would have been a simpler solution, but I have never incorporated relays in a circuit before, and I am so pleased with the result.
I appreciate your concerns about my inexperience in electrical/electronic ways but perhaps I undersold myself. I may not be able to design a circuit (I have followed Polyglot in his quest for an F-stop timer with admiration, and know T Kamiya also understands electronics). But I think I have a pretty healthy regard for the dangers of mains electricity especially when next to water, and understand insulation and secure connections. I am a recently retired Consultant Surgeon and wouldn't dream of switching anything on until I have been over it thoroughly with my AVO meter. So I know enough to understand your concern about amateurs dabbling with electricity; I thank you for those concerns and also your input which gave me the confidence to go ahead.