Interesting, but hardly surprising: The system currently likely altogether lacks any connection with your old passport and any/all details that were the basis for it being issued in the first place. You therefore basically have to start afresh as if you were effectively a non-existent individual needing to prove what/who he/she is. Based on other recently highlighted examples, it is not impossible that you will be unable to convince the UK system that you exist, never mind who you really are and least of all that you "belong". It can be entirely irrelevant that you have attended education establishments in the UK, paid tax in the UK, etc., etc., including having held a UK passport. This is what makes the UK different (superior ?) from other European (and beyond that) countries - the system is incompetent.