Oldest stock still in passenger use

[LondonLarry]

I know what "mainline" means. What I'm trying to understand is why folk are assuming that the OP is only interested in mainline stock, especially as there is some seriously old stock still in passenger-carrying service on other non-mainline railways.

O L Leigh

I hadn't realised my original post would generate so many comments!

By "regular passenger use", I had originally thought about trains on the National Rail network (i.e. excluding heritage/preserved lines). However, I've read all the comments about heritage lines with interest.

I'm only interested in "mainline" which for me would exclude underground, tram, heritage/preserved railways.

Thanks for all your comments!