The Working Time Regulations (WTR) came into force in 1998, implementing the European Working Time Directive (WTD), now under review by the European Commission. 

A “rolled-up” rate for holiday pay

In typical types of employment, particularly short-term, seasonal or casual employment, it may often be advantageous for the employee or worker to know that his or her holiday pay is secure by being paid on an accruing pro-rata basis during the period of this employment, thus avoiding a dispute about such payments with an employer at the end of such short-term employment.