His employer is required, by law, to provide him with a contract or job description within a few weeks of starting work. This should explain how much notice is required.
In the absence of such a document, then the stantard is that his notice period is the same as his pay period...
His pay situation is also very odd. He should be paid weekly OR monthly - as defined in the document above - and is legally entitled to recieve payslips showing pay and deductions. He should check with the tax office that he has had tax properly deducted. If not, he is building up problems for his future if he doesn't sort it now; and his employer is deep in the mire. Is he properly paid for holidays?