Thank you very much for clarifying. First of all, I am sorry to hear about the issues you have experienced in your situation.
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, once you have gone through the grievance process, you are left with limited options to take it any further and as you cannot claim for bullying alone, you will have to resign and claim constructive dismissal instead.
It is also worth mentioning that there is a possible alternative solution to this, which could avoid the need for legal action. That is where the employer is approached on a 'without prejudice' basis (i.e. off the record and with protection against these discussions being brought up in future legal proceedings) to try and discuss the possibility of leaving under a settlement agreement. This can be done by asking for a meeting, or it can be done in writing, via letter or email. Under a settlement agreement the employee gets compensated for leaving the company with no fuss and in return promises not to make any claims against the employer in the future. It is essentially a clean break, where both parties move on without the need for going to the Employment Tribunal. However, it is an entirely voluntary process and the employer does not have to participate in such negotiations or agree to anything. There is nothing to lose by approaching this subject with the employer and testing the waters on this possibility - the worst outcome is they say no, whereas if successful it can mean being allowed to leave in accordance with any pre-agreed terms, such as with compensation and an agreed reference.