Yes it is. Under the Part time Workers (Prevention of Less Favourable Treatment) Regulations, workers have the statutory right, as part timers, to be treated the same as comparable full time workers, that is, workers on the same type of contract with the same employer. This is a right you enjoy from day one of your employment.
If you think you’re receiving less favourable treatment from your employer as a part timer, you are entitled to receive, on request, a written statement of reasons for this. This statement may be taken into account by an employment tribunal. The employer has to prove that this different treatment is justified on objective grounds.
For more information, see our part time workers’ section.