There are general rules about pensionability which were best summarised in the recent report of the commission on public service pensions. The report states that:
The general rule under public service pension schemes is that allowances in the nature of pay are pensionable if they are of a permanent nature or are for extra or inconvenient hours of duty, if a regular and recurring feature of the job and a compulsory condition of service, e.g. unsocial hours duties and shift allowance.
The report goes on to rule out the possibility of extending pensionability to overtime generally. While there may be instances where overtime is pensionable it applies only if that overtime is compulsory.