If you are still in employment, you might want to consider raising a grievance regarding these unlawful deductions from wages/non payments.  A grievance is simply a written letter or note to your employer setting out the issue you are concerned about, ie. “I received my payslip and have not been paid for holidays/last week’s overtime/notice pay, etc.  Further information on how to raise a grievance can be found on the ACAS website.
If your employment has ended, you might still want to consider writing to your former employer and if you do not receive a response or you receive a response which is unsatisfactory to you, your options would be to issue a Notice of Intention to Claim to ACAS Early Conciliation.
The time limit for issuing a Notice of Intention to Claim to ACAS is three months less one day from the last deduction.
For any further legal advice regarding your matter please see our employment law pricing and services.