Flexi duty allowance explained: the 20% Grey Book supplement

What the flexible duty system is

The Grey Book lists several national duty systems: shift, day-crewing, day duty, flexible duty and retained. The flexible duty system applies only to employees in the roles of Station Manager and above. Employees on it perform two types of duty: managerial duty, which is rostered for operational command, managerial, supervisory or specialist work (also known as positive hours), and standby or call-out duty, when they are on call to perform managerial duty urgently if needed.

Transfer onto the flexible duty system is voluntary. The Grey Book says that, in view of the pension implications, employees will not be transferred from the system against their will, except as a result of a disciplinary reduction in role to a level where there are no posts in that service on the flexible duty system. Employees are notified of the geographical area in which they must be based for standby duty, and may have freedom of movement within it.

The system is often called flexi duty or FDO (flexible duty officer) duty. The ranks and career progression guide explains the roles that use it, and firefighter pay progression shows the pay points.

The 20% supplement

Grey Book Section 3, Part B says that an employee on the flexible duty system shall be paid a pensionable supplement of 20% of basic pay. Three features matter. It is a percentage, so it rises when basic pay rises: the 3.8% award of 1 July 2026 raised the supplement by 3.8% too. It is pensionable, so it increases the pay on which pension contributions and benefits are calculated. And it is a supplement to basic pay, not part of the NJC basic figure, so the national tables do not include it.

London Fire Brigade's Policy 558 shows the same 20% at work in its own scale for Station Commanders and Group Commanders: a Station Commander B Competent on £64,589 basic receives £12,917.80, a total of £77,506.80, and a Group Commander B Competent on £73,631 receives £14,726.20, a total of £88,357.20. LFB also publishes an hourly rate for these ranks of £35.39 and £40.35, which is calculated from the total, not the basic.

The Grey Book text says nothing about a supplement for Crew Managers or Watch Managers, because the system does not apply to them. Those roles are on shift, day-crewing or day duty systems, and receive overtime instead of a supplement.

How the flexible duty rota works

The Grey Book sets the rota principles. The sum of the rostered managerial duty hours and the rostered standby hours divided by four must average 48 a week over a cycle not exceeding eight weeks. No rota may contain more than five consecutive 24-hour periods during which duty of either type is performed, and in any two-week period starting on a Monday there must be at least two pairs of rota leave days. Managerial hours must not average more than 42 a week, and the total of both types of duty must not average more than 78 a week.

So the 48-hour week counts standby time at a quarter. An officer with 36 managerial hours would have 12 weighted hours left, equal to 48 standby hours. That is how a rota reaches 48 weighted hours while total hours on duty can be much higher, up to the 78-hour average limit. Rota leave must be rostered no less frequently on a Saturday or Sunday than any other day.

This is a rota design rule, not a contract for your individual case. The detailed arrangements for how your service rosters flexible duty, what standby means in practice and any recall provisions are local. For the equivalent rules on other systems see day crewing and other duty systems.

Worked examples: what the supplement is worth

Take a Station Manager Competent A on £53,604. The supplement is £53,604 × 0.20 = £10,720.80, taking pay to £64,324.80. On the site's 2026/27 England model, pension at 14.09% is £9,063.36, income tax £9,536.57 and National Insurance £3,297.10, leaving £42,427.77 a year (£3,535.65 a month). Without the supplement the same Station Manager takes home £36,272.28 (£3,022.69 a month), so the supplement adds £6,155.49 a year net.

Take a Station Manager Competent B on £57,402. The supplement is £11,480.40 and total pay £68,882.40. That total exceeds £66,908, so the model applies the 15.59% pension band to the whole pensionable pay: pension £10,738.77, tax £10,689.45, National Insurance £3,388.25 and take-home £44,065.93 (£3,672.16 a month), against £38,806.61 without the supplement, a difference of £5,259.32. The net gain is about 45.8p per £1 of supplement.

For a Group Manager Competent A on £61,736 the supplement is £12,347.20, total £74,083.20, and the model gives take-home £46,595.91 (£3,882.99 a month), against £41,145.12 without it. The gain is £5,450.79, about 44.1p in the pound. As pay rises through the bands, more of each pound goes to tax, National Insurance and pension.

These figures show why the supplement is often described as worth roughly half its face value after deductions at these pay levels. They also show why comparing a flexible duty post with a shift-based one needs care: the supplement compensates for standby duty and the rota's demands, not just for higher responsibility. Ask to see the rota, the standby area and the call-out expectations for the post before you volunteer.

Overtime, time off in lieu and public holidays on flexible duty

The overtime rules in the Grey Book apply to Watch Managers and below and, for casual overtime, to Station Managers not on the flexible duty system. So a Station Manager on flexible duty is not paid overtime for staying on at an incident. The Grey Book instead says that where an employee on the flexible duty system is detained at an operational incident beyond their normal rostered duty time and requests compensatory time off in lieu, the request shall not unreasonably be refused.

Public holidays work differently by level. A Station Manager on the flexible duty system who is required to work on a public holiday is granted one and a half days' leave in lieu, while a Group or Area Manager is granted a day's leave in lieu. Station Managers not on flexible duty are paid double time and granted a day's leave in lieu, and the double-time payment is not pensionable.

Recall to duty for a serious incident is voluntary and paid for a minimum of three hours at double time; Group and Area Managers who are recalled are paid at the maximum rate applicable to a Station Manager. See bank holiday pay and firefighter overtime rates for the detail.

Pension and tax effects

Because the supplement is pensionable, it raises your pensionable pay, which affects both your contribution rate and your benefit. A higher salary can push you into a higher contribution band. In the Station Manager Competent B example, adding the supplement lifts pensionable pay above £66,908 and moves the contribution band from 14.09% to 15.59% on the site's model. The contribution is deducted before income tax, so it reduces tax as well.

The higher total may also increase income tax through the 40% band, which starts once taxable pay after the personal allowance exceeds £37,700, and increases the National Insurance charged above £50,270 at 2%. High earners should also be aware of pension annual allowance and other limits, covered in the guide to firefighter pension annual allowance tax, and of the high-income child benefit charge; see the child benefit guide.

The Grey Book also says that an employee who has been on the flexible duty system cannot be moved off it against their will for the pension reasons it gives, so a decision to join is a long-term one. Consider your pension position before volunteering, and use the pension calculator to see the effect of a higher pensionable pay.

Temporary promotion and acting up onto flexible duty

If you act up or are temporarily promoted into a flexible duty role, the treatment of the supplement is a local matter and worth checking. Services may treat the supplement and its pension status differently for an acting period. This guide does not state a national rule, because the Grey Book text on acting up does not mention the supplement.

The Grey Book's acting-up provisions say an employee required to undertake the duties of a higher role is paid the basic hourly rate for the development phase of that role, or the competent rate if they have demonstrated competence in it, and must have demonstrated competence in their current role, shown potential to develop and completed the relevant assessment process. Ask your service in writing how it treats the supplement, the pension position and the dates.

Read the acting-up pay guide for the general rules and the promotion calculator for comparing pay points. For a personal written summary, the paid Personal Pay Report sets out how your pay, deductions and supplement fit together.