Now this was never meant to be a competition for the best tip, just a cry for help in my frustration. But I have to say that the most useful, and certainly the cheapest, tip so far is the one from mwdake in post #23 above.
That is to cut a piece of film box cardboard to the width of the film and insert it in the reel before turning off the light to use as a guide to start the film. So far I have used it three times with instant success every time. I found that it works better with the Paterson reel than the Jobo one because it has its ball bearing "grippers" about 2.5cm into the slot, whereas the Jobo reel has little "chicanes" right at the start of the slot which prevent the thickness of the cardboard entering the slot.
Thanks to everyone who suggested stainless steel, particularly Hewes reels. There will be one in my future, but for the moment plastic and cardboard is doing the job.