No idea, but the Highway Code refers to "authorised persons" being allowed to give signals and instructions and this includes traffic wardens and lollipop ladies
In this case I was not going to give him any leeway
Locally we've had lots, and I mean LOTS, of abuse of 'powers' by CSOs and real live police (though they are so rare as to be an endangered species.) Flexing their muscles on private property, enforcing bylaws they aren't empowered to enforce, getting stuff plain wrong and then making up utter BS post-hoc to try to justify themselves. One is on a one woman zero-tolerance campaign to rid the town centre of cyclists, even maiden aunts with baskets on their way to church, even when they are cycling legally!
I had a recent encouter much along the lines of yours, sans real copper, I dismounted, walked three paces and in full view of her got back on
Her: Oi! I told you to get off your bike
Me: (trackstanding) You said I could get back on when it was safe, it's safe so... I'm... off...
rides off like he stole it....
The trick hereabouts is not to ride the same bike into town two days running. This particular 'lady' seems to only remember my mtb after a strange encounter (recorded elsewhere) in the park at night where she unilaterally decided my practising manuals was against the byelaws as it was dangerous.