I thought I would post this up as the employer of a friend of mine tried to force him to take holiday leave when he was absent from work due to sickness. Always useful to know your rights.

Workers who fall sick during their annual leave are entitled to take corresponding paid leave at a later date, the EU's top court has ruled.
"The right to paid annual leave cannot be interpreted restrictively," the court says. The UK does not have an opt-out in this area of EU labour law.
The court in Luxembourg said the EU Working Time Directive grants workers a right to at least four weeks' paid annual leave "even where such leave coincides with periods of sick leave".
The ECJ says "the point at which the temporary incapacity arose is irrelevant".
"Consequently, a worker is entitled to take paid annual leave, which coincides with a period of sick leave, at a later point in time, irrespective of the point at which the incapacity for work arose."

If ever in doubt always worth a visit to your local GP to cover yourself.