Retro...with respect, I think you have the old Post Office pension wrong. It was never "non-contributory" but was a standard superannuation type. It was identical in every way to a Civil Service scheme, which most other Public Service employers followed, like Postmen, Teachers, Local Government, etc.
This "superann" scheme typically made employees paid about 6% of their salaries into the scheme....the exact percentage differs from employer to employer, and from time to time. The employer then paid in as well, and the resultant final pension was worked out from final salary and years in service.
It was normal for people to "take their pension with them" so to speak, when they changed jobs within the Public Sector. When I was a young apprentice, we had quite a lot of engineers that came from the railways, ie British Rail, and also from the Gas and Electricity Boards. As the pension schemes were the same, accrued years and benefits were amalgamated into our scheme.
I repeat...these schemes were never non-contributory.
I would like to congratulate you on your marked improvement in space bar use ! We seem to have fallen out over this issue, which was never my intention, I assure you. It just makes any print easier to read, that's all. Just like Mission Impossible, your task now, if you choose to accept it, is to explore the many uses of paragraphs !