All employers in the construction industry have to register their employees with CWPS and pay contributions. The employer and employee pay a contribution, it would be on your brothers payslip. Sick benefit is part of this contribution that is paid and as the previous poster said you are entitled to 10 weeks of holiday pay.I dont think that employers are obliged to be members, I believe that all contrustion workers are to be part of the CWPS, no exceptions.
Double check if brother is paying these contributions or maybe ring the CWPS and see if his employer is paying his contributions. All employees are entitled to get a statement from the CWPS to see if there contributions are being paid.