Sorry, I'm not very good at using this list but I want to reply to Dawn and thank her for the detailed info - and to others who replied. I have written to various places over the years and I think that includes GRO, all with no result or no reply at all.
Dawn, you give me renewed hope. I have the long form birth certificate for my father and it does have (as you say it should) an additional annotation 'Adopted' and signed by the Superintendent Registrar. This annotation is not dated but the Superintendent Registrar in question was Tom Percival and I know (from reading Jenny Keating's book on Adoption in England 1918-45) that this guy was active in the Tynemouth 'adoption industry' at the time my father was born. So I assume my father was adopted soon after birth not at an older age. Certainly he came into the care of the person who raised him as a baby because I have a photo to prove it.
Dawn, you say you have access to GRO adopted children Index at the Archives in London. Is it possible for you to look up Edward Davison born Tynemouth on 5 March 1918 to James and Hilda Davison. He presumably was adopted soon afterwards, and was later known as Robert Hull, also (after 1940) as Robert Edward Davison Hull. The person who raised him was Lillian Baxter Hull, married to Harry Hull (died Oct 1918) both of Leicester. Another person who claimed Edward Davison was his 'adopted son' was Herbert Victor Collison, also of Leicester. If you can find any of these names, anywhere, on any adoption records, I would be eternally grateful.
Thank you.