If he has been continuously employed at his place of work for less than 2 years then his employment rights will unfortunately be somewhat limited. Most importantly, he will not be protected against unfair dismissal. This means that his employer can dismiss him for more or less any reason, and without following a fair procedure, as long as their decision is not based on discriminatory grounds (i.e. because of gender, race, religion, age, a disability, sexual orientation, etc.) or because he was trying to assert any of his statutory rights (e.g. requesting paternity leave, etc.). In the event that the reason for dismissal fell within these categories, then the dismissal will either be automatically unfair, or there will be a potential discrimination claim.
If the dismissal had nothing to do with any of the above exceptions then he would not be able to challenge it and his only protection would be if he was not paid his contractual notice period, because unless he was dismissed for gross misconduct, he would be entitled to receive his contractual notice period. If he did not have a written contract in place he would be entitled to the minimum statutory notice period of 1 week. His employer would either have to allow him to work that notice period and pay him as normal, or they will have to pay him in lieu of notice.
If he was not paid his notice period when he was due one, that would amount to wrongful dismissal (which is different to unfair dismissal) and he could make a claim in an employment tribunal to recover the pay for the notice period that he should have been given. There is a 3-month time limit from the date of dismissal to submit the claim.
This is your basic legal position. I have more detailed advice for you in terms of the steps he needs to take if they did not pay him what he was due, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you