Employers are not permitted to make deductions from wages unless the employee had previously been provided with a contract specifically stating the reasons for which such deductions may be made:
http://www.direct.gov...ployees/Pay/DG_175878
If payment is not forthcoming your son should send a written demand for the money which is owed to him. That demand should:
(a) show his name and address ;
(b) show the employer's name and address ;
(c) be dated ;
(d) clearly state the amount demanded ;
(e) clearly state the reason for the demand ;
(f) indicate that if payment is not received within a specified period (I suggest 14 days) your son will commence legal action.
(g) be sent by recorded delivery.
If payment is still not forthcoming, your son should make an online claim against his former employer:
https://www.moneyclaim.gov.uk/web/mcol/welcome
Chris