Brake lights staying on, but not the switch this time

Morning all, I hope the holiday season is going well for you.

The brake lights were permenantly on my car. It is a 1996 VVC, and it has the black plastic, ratchet-type of switch. I have had this issue before, a few times, most recently when my MoT tester (who is a big lad) clipped the brake pedal with his size 11's while getting out of the car on test and caused the usual problem. I have reset the switch a half dozen times in the eight years I have had the car; while it's not exactly fun bending yourself to get in there, it's not the end of the world.

However, last week the brake lights came on again. Resetting the switch made no difference, and I figured that at 26 years old, the original one was probably FUBAR and due replacement. My local motor factor sourced a new one, which I duly fitted, and the brake lights were still on.

So I reset it a few times, with no change. Then refitted the old one, no change, then fitted the new one back on again, still no change.

I read up on the switch again, in case I had forgotten something, but no, the switch is reset by drawing/pulling the plunger out, then re-fitted while holding the brake pedal down . So i did that again and the brakes ights are still on.

So I started playing with it all, and quickly discovered that by lifting the pedal slightly (towards the driver), the brake lights go out. I thought this was a no-no, given the switch design and the way it is supposed to work?

Anyway, bodge time as I needed the car to get to work. it currently has a bungee doing "additional return spring" duty which is working fine, and the brake lights are only on when I brake. The brakes themselves feel fine, and I can't see a missing or slack spring anywhere on the pedal assembly.

Am I missing something basic?