Thank you very much for clarifying. First of all, I am sorry to hear about the issues you have experienced in your situation.
This would appear to be a case of bullying. Workplace bullying is unfortunately a rather common problem, which occurs more often than it should. What makes it even more difficult is that there is no specific legislation that deals with it, meaning there are limited options for the victims of bullying to take things further legally.
Although there is no legal definition of bullying, the Advisory, Conciliation and Arbitration Service (ACAS) defines it as “offensive, intimidating, malicious or insulting behaviour, an abuse or misuse of power through means that undermine, humiliate, denigrate or injure the recipient.” Examples given are: spreading malicious rumours, or insulting someone by word or behaviour; exclusion or victimisation; unfair treatment; overbearing supervision or other misuse of power or position; making threats or comments about job security without foundation; deliberately undermining a competent worker by overloading and constant criticism; preventing individuals progressing by intentionally blocking promotion or training opportunities.
Under law, specifically the Health and Safety at Work Act 1974, an employer has a duty to ensure the health, safety and welfare of its employees. In addition, they have the implied contractual duty to provide a safe and suitable working environment. That includes preventing, or at least effectively dealing with bullying behaviour occurring in the workplace.
In terms of what the victim of bullying can do to try and deal with such problems, the following steps are recommended (I appreciate you have already followed some but I should cover them all anyway, just in case):
1. First of all, and if appropriate, the victim should try to calmly and professionally resolve the issue informally with the person responsible for the bullying. I do, however, appreciate that this is much easier said than done.
2. If the above does not work or is not a viable option, the victim should consider raising a formal grievance with the employer by following the company's own grievance policy, or sending a complaint in writing to their line manager. This formally brings the bullying issue to the attention of the employer and they will have a duty to investigate and deal with it.
3. If, following a grievance, the employer fails to adequately deal with the bullying issues, the victim would need to seriously consider their next steps. Unfortunately, employment law does not allow employees to make a direct claim for bullying. As such, the most common way of claiming is by resigning and making a claim for constructive dismissal in an employment tribunal. The reason for resigning would be to claim that by failing to act appropriately, the employer has breached the implied terms of mutual trust and confidence and failed to provide a safe working environment and that there was no other option but to resign.
As a final pointer, the victim should try and gather as much evidence as possible before considering making a formal complaint and certainly before going down the resignation route. As bullying is often verbal or through actions, the best way is to keep a detailed diary of all bullying occasions so that there is at least some reference in written form that the employer and/or the tribunal can refer to.
You can also refer to this guide by ACAS which deals with unfair treatment at work – the following is a direct download link: