50p pay rise taken away

[GreenTurtle1]

Asking on behalf of some else.

Is it legal to have pay reduced for not doing your job correctly?

I would have thought issues like this should be dealt with during supervision to help the employee improve?

Was the pay rise given to everyone or was this person promoted with a pay rise. Is there any contract to say if it's permanent or temporary and are they being demoted, had any supervision, knew in advance it was for a trial period. Also, are they in a union.

As far as I know it was a permanent pay rise and there has been no demotion.
Supervision's haven't been carried out she was just informed of the fact. They aren't part of a union unfortunately