We are considering introducing a scheme to allow staff to buy up to 5 days of additional holiday per year. Does anyone have advice on drafting a policy for this?

Questions I have thought of are:

Do we allow this on an ad-hoc basis and treat it as unpaid leave making deductions from pay each time?
Should we treat this as an arrangment that can only made once each year and if so, is the cost of the extra days treated as a reduction in salary (surely pension, PHI implications) and as such monthly pay reduced, or deducted in the month that the holiday is taken?

Lots of questions, I know, and I would really appreciate advice from anyone who has implemented such a scheme. We don’t offer a flexible benefits scheme but we do offer voluntary benefits.

Thank you all in advance
Sue