In some circumstances, your employer may be able to justify paying different rates of pay because you are learning your job. Discrimination law can be complex area, so it's a good idea to seek advice if you feel you are being discriminated against.
Similarly, it is unlawful for employers to pay staff employed on fixed-term contracts less than permanent staff for doing the same or a similar job.
It is unlawful for an employer to discriminate on pay and other conditions of employment on grounds of age, disability, race, being transgender, marriage/civil partnership, sex, maternity/pregnancy, religion or belief, or sexual orientation. Women are also entitled to the same rate of pay as men (and vice-versa) for doing the same or similar work and to equal pay for equal value work.
Most workers have rights not to be discriminated against, including agency workers, those employed via contractors, trainees, and some individuals who are self-employed and offering services in a personal capacity.