Employees, casual workers and temps are all entitled to holiday pay, with the entitlement accruing from the beginning of employment.
If you are one of the many employers who roll holiday pay for such short-term workers into their wages, rather than paying specifically for the time off, you will have to change your practice, because the European Court of Justice has recently ruled that 'rolling up' holiday pay is contrary to the Working Time Directive and therefore unlawful. Even if there is no prospect of short-term or casual workers taking holiday while in your employment, you need to be able to identify the holiday element in their wages packet, and you may have to amend your short-term contracts. If you are in this position, take legal advice.