Public services union Unison took an important case to the European Court on behalf of commission workers, and as a result, the European Court has confirmed that holiday pay must include commission. This means that your holiday pay must include an element for the commission that you would have earned if you had been at work generating sales, instead of being on holiday.
It is unlawful, following this ruling, for your employer to pay you holiday pay based on basic pay only, excluding commission. Speak to your union if you are concerned about how holiday pay is calculated where you work.
Strictly speaking, the ruling applied only to the four weeks of holiday given to workers by the European Working Time Directive. However, most fair and sensible employers will apply the same method to calculating holiday pay for all types of holiday.