I have No 79699 issued in 1968. It is not clear that it is a lifetime PPL but, when I revalidated it after a 23 year break in 1997, the new one states clearly "for the holder's lifetime" but has a new number.
The original PPL looks like it was renewed after 5 years, in 1973, for another 5 years. I don't remember having to pay anything at the time. probably just satisfied them that I had kept up my C of E for the five years. If you didn't, you needed a new test.