I should probably have mentioned that the main problem I had was with a patchwork blanket where there were over 60 squares with 2 ends to each square to fit in, with no real 'seams' as such, as I sewed them quite flat. I have since made some sweaters which were not nearly so problematic because of fewer ends and of course you can sew them right into the seams if necessary, and I have found that sewing them so that they double-back on themselves (eg. across the seam to the other half of the sweater) really helps. Thought I should point that out in case I have accidentally started a cotton-panic!
However, the FrayCheck sounds like a great idea, I haven't heard of that before (unless it has a UK name that I haven't connected in my head), but I shall go away and look it up. Thanks very much!