If you feel you are treated unfairly at work you can take out a formal grievance, setting out why you are unhappy with your employer or your working conditions. There is a statutory minimum grievance procedure which employers must follow, but most good employers will have their own.
If you ultimately feel you have no alternative but to resign because of your employers' conduct towards you, then your resignation may constitute a constructive dismissal. In such circumstances you can apply to an employment tribunal claiming unfair dismissal. Strict time limits apply: you must normally bring a claim against your employer on Form ET1 within 3 months of the date that your employment terminated.
For claims made before 4 July 2009, based partly or completely on events which took place before 6 April 2009, you must follow the statutory grievance procedure first, giving your employer 28 days to respond. Otherwise, the employment tribunal could strike out your claim. This will no longer apply to claims lodged from 4 July 2009.