A full update on the plumbing:
Initial problem - the 15mm copper pipe that runs along a wall to the toilet had been damaged and was leaking c. 2l a day into a plastic box placed under it.
Steps taken:
1) Turn of water using in-line valve under kitchen sink leading to total failure of control valve so water gushing into under sink cupboard. Contents of cupboard all over office floor.
2) Water off at fortunately fitted extra control valve.
3) Cycle to Wickes. But new control valve and new grips.
4) Remove waste pipes from sink so broken control valve can be removed.
5) Remove control valve. Realise that olives wont' come off so cut back pipe. Now new control valve won't fit.
6) Cycle back to Wickes. Swap control valve for flexible connector because I'm not prepared to measure anything
7) Fit flexible connector.
8) Turn water back on next morning. Check new connector. All good. Do some actual work in another room.
9) Staff member starts, tells me that toilet floor is sopping wet.
10) Discover toilet cistern - which hasn't been touched - now doesn't fully shut off when cistern is full. Also notice for first time that overflow is not connected to anything so overflows onto the floor.
11) Turn off water at control valve hoping it doesn't fall apart. Luckily it doesn't
12) Cut out broken pipe (the original job) with hacksaw (now retrieved from home)
13) Clean x decades of paint from pipe end
14) Realise that I will have to replace the section in two parts because it passes through a door frame and there isn't enough room to put in one piece. (Discover on removing old pipe that the join was hidden by the frame, and that was what had failed)
15) Cut two sections of pipe. Connect one to the sawn off end, and the other to it. On a roll at this point although I did lose an olive somewhere.
16) Go to local hardware shop to get replacement ball cock thing for cistern
17) Return with what looks like an identical ball cock thing only to discover that the bit the float attaches to is very marginally wider than on the old one,. so trim that down with a box cutter. Attach float. Offer up ball cock thing. Discover that the whole assembly is imperceptibly wider than the previous one and the float gets stuck. Try to use valve from new one with the rest of the old one, but the arm attachment is also different.
18) Go to Wickes again as they do another ball cock thing that looks like the one that was fitted originally, and because I also need a bit of flexible pipe to attach ball cock thing to the new pipe - hardware shop didn't have any. I do like a flexible pipe as it saves measuring - did I mention that? Determine that ball cock thing need a 1/2 inch connector. Buy it, and connector.
19) Back to work, try and fit new ball cock thing. Discover it has an entirely different float connector to the original that no amount of adjusting with a box knife will make work, but fortunately I am able to fit the 'arm' from the old one. Assemble it, fit it. Get flexible pipe. Discover that despite knowing I wanted a 1/2 inch one, I have somehow brought home a 3/4 inch one that presumably was on the wrong bit of display.
20) Return to Wickes, swap flexible pipe. I know a this point from measuring the gap with the wrong pipe that a 500mm one is not quite long enough to reach the end of the pipe, but a 1000mm will be far to long and end up being kinked. As I am going to need to put in a bit more pipe (coming up from the end at right angles toward the cistern) but have no pipe left, I look at their pipes. Decide that for the short amount I need it's not worth buying a full length section, but that's all they have. Buy 300mm connector with correct 1/2" / 15mm fittings.
21) Attach flexible pipe to ball cock device. Attach right angle fitting to end of pipe. Fish removed pipe from bin, cut out c25cm of good pipe away from the damaged area, remove x years of paint and attach right angle fitting to flexible pipe.
22) Turn water on and retire a safe distance.
It all seems ok this morning ...