Brake lights will not activate on tne move unless the brake pedal is pressed, or in an EV when slowing using regen beyond a certain level.
When stationary they will only activate with the footbrake. Con and use and Vehicle Lighting Regs dictate all that malarkey.
I never did, but a colleague of mine once stuck someone on for using lights to dazzle by holding on the footbrake - then offence is clear cut, along with not being in proper control. That was the 90s when folk were still more disciplined with correct handbrake usage. Sadly, like footway parking and parking facing into the traffic flow at night, so many twits do it its now simply unenforceable,