Your friend might have a 'zero hours' contract. This is the type of contract which is most commonly used by those employment agencies which supply temporary staff to employers. With such a contract the worker is an employee (rather than self-employed) but has no defined hours. If so, he only has to be paid for the hours he actually works.
However, if his contract with his employer is of the 'normal' type, the rules relating to being 'laid off' apply. (An employee always has a contract with his employer, even if nothing has ever been put into writing).
The rules relating to temporary lay-off state that your friend should receive full pay unless the terms of his contract state otherwise. Even if there's no contractual right to be paid during a lay-off, your friend is probably still entitled to receive Statutory Guarantee Pay (of just over �20 per day) for a maximum of 5 lay-off days in any 3 month period. He might also be entitled to receive certain state benefits. See here:
http://www.direct.gov.uk/en/Employment/Redunda ncyAndLeavingYourJob/DG_10026693
Chris