My son started work for a double-glazing firm a month ago on a self-employed basis. He is supposed to be paid weekly, but although they are promising to pay him he has yet to receive any money.
If your son has to work as and when directed by the firm it’s likely that he is employed, not self-employed. This is an important distinction, since self-employed people have no employment protection. If the situation continues he can apply to an employment tribunal for a ruling as to his employment status and for his pay. If the tribunal accepts he is employed by the firm it could order them to pay him compensation. Alternatively he could bring a claim for his money in the small claims court.