It is important that employers are transparent when it comes to explaining payment to employees. Employees must receive the agreed wage for the work undertaken, in line with employment contracts and conditions of employment. Very few issues cause so much angst as issues surrounding money and they could lead to a break down in the employer-employee relationship if not handled correctly.
If you have concerns about your pay or deductions therefrom, you should in the first instance speak with your employer. You can request from them details of how your wage has been calculated and why certain deductions have been made.
If you do not received satisfactory explanation from your employer, you can raise a claim with an Employment Tribunal even whilst employed. However, if you have left your employment, you must bring any claim within 3 months of the end of your employment.