Hello my name is ***** ***** I am happy to help you today. How long ago was the last time they failed to pay him in accordance with the original contract?
They have not paid him the full amount for as long as he has been working there
In that case he can bring a claim in breach of contract and for unlawful deduction from wages. He should write first asking for them to pay within 7 days. If they decline to pay he can eitehr raise a claim in the county court or in the employment tribunals using the form he will find at www.employmenttribunals.gov.uk.
If you have any further questions please do ask.