This morning's commute and other commuting stories

If you dismount you are a pedestrian and can do what you like.

Not quite. You're a pedestrian propelling a vehicle. The bike doesn't disappear when you dismount it. This is the common misinterpretion of the Crank vs Brooks ruling.

If you are cycling it's the same, it's sometimes ambiguously marked for cyclists but if it has a clear stop line or kerb where a stop line could be then that's that I'd think as the law broken when jumping the lights is "ignoring a traffic signal" which all the lights could be taken as.

The RLJ offence is (paraphrased) "propelling a vehicle across the stop line on a red signal". Hence my question about whether there is a stop line or not. Which is why crossing a toucan crossing (or even a puffin/pelican crossing) from side to side (so not crossing a stop line) can be done regardless of the crossing signal.