Bullying at work involves repeated negative actions and practices that are directed at one or more workers. The behaviours are unwelcome to the victim and undertaken in circumstances where the victim has difficulty in defending themselves. The behaviours may be carried out as a deliberate act or unconsciously. These behaviours cause humiliation, offence and distress to the victim. The outcomes of the bullying behaviours have been shown to cause psychological distress which affects social and work behaviour.
But even if something could be defined as bullying doesn't mean there's necessarily a legal claim to be made or compensation available.
If the person feels they have been driven to leave their job, and claim constructive dismissal, if they win that claim (tricky to do) then compensation would be based on financial loss only. If it could be discriminatory bullying, ie related to gender, race, ethnicity etc, then there might be more compensation available.
Log everything, collect as much evidence as you possibly can. If they are giving you formal warnings then this should be through the disciplinary procedure and you should be allowed a colleague or trade union rep to accompany you .... if they are not letting you then do not say anything in the hearing apart from 'I would like my rep please' keep repeating yourselve if need be.