It's a while since I visited the forum. Oxford Guy: next time I'm in Oxford visiting the rels I'll message you and bring the extractor down.
What saddle are you using? A Brooks is 1" higher than most plastic saddles. I can tell if my saddle is a mere 5mm off correct height* but it just might work.*this sounds ridiculous but most cyclists who ride regularly will feel if it's not right - and you have to correct for crank length too, if different bikes have different length cranks. For instance, I have saddle height of 30.25" with 170mm cranks but I increase that by 5mm (to almost 30.5") for 165mm cranks so the leg extension at the bottom of the stroke is identical.