SiteYour electrician handed in their notice on Friday. Four weeks, then they're off to a site ten minutes closer to home.
By Monday morning you've got two options on the table. HR wants to advertise the job straight away. The ops director wants to know why you can't just "get an agency sparky in". Both want an answer by the end of the week.
You know the real question sits under both. What does the site need for the next six months, and what does it need for the next five years? The two answers are rarely the same.
Start with how long the gap will last
The single biggest factor is time. Be honest about it.
A gap of a few weeks, such as holiday cover, a short sickness or a planned shutdown, is agency work. Nobody hires a permanent engineer for a fortnight.
A gap with no end date, because someone has left and the work hasn't, is a permanent job. Agency cover can bridge it while you recruit, but it shouldn't become the plan.
The awkward one is the gap you can't size. A long sickness. A new line that may or may not get a second shift. Demand you're not sure will last past Christmas. Most sites get this one wrong, usually by drifting. They book agency cover a week at a time and look up six months later.
The 12-week rule changes the sums
Agency engineers start with some rights on day one, such as the same access to canteens, car parking and other shared facilities as your own staff. After 12 weeks in the same job, they qualify for what GOV.UK calls equal treatment. That includes "'equal pay' - the same pay as a permanent colleague doing the same job", plus automatic pension enrolment and paid annual leave (GOV.UK, agency workers' rights).
So if your own electricians get a shift premium and overtime rates, the agency electrician on the same work gets them too from week 13*. Add the agency's margin on top and long agency cover gets expensive.
We've set out exactly how the clock counts, and what pauses it, in the 12-week rule: what changes on day 85. If you expect the cover to run past three months, read it before you book.
What agency cover does well
Agency cover is fast. A good agency can have an engineer on site in days, sometimes hours. Recruiting a permanent engineer can take months, and the person you offer may still have a month's notice to work.
It's flexible. You can scale up for peak and back down in January. You aren't committing to a salary for a role you're not sure you'll need.
And the agency does some checking for you. Before it supplies anyone, it must confirm their identity and that they have the experience, training and qualifications you've said you need (Conduct Regulations 2003, regulation 19). That only works if you tell the agency what you need. Ask for "electrician" and you'll get anyone. Ask for "multi-skilled, 18th Edition, Siemens S7, used to servo drives" and you'll get someone who fits. Our post on what agency fees actually pay for explains what else you should expect for the money.
What a permanent hire does well
A permanent engineer learns your kit. In a year, they know which sensor on the case erector drifts when it's cold and which gearbox runs hot in July. That knowledge is worth a lot at 3am.
They also own the work. A permanent engineer improves the PPM, chases the repeat faults and trains the apprentice. Cover engineers can be very good, but they're rarely around long enough to fix the causes.
There's the cost side too. Over a full year, a permanent salary usually works out cheaper than paying an agency rate for the same hours. The catch is that you pay it whether the work is there or not.
Whatever you choose, check competence
Agency or staff, the legal duty on competence doesn't change. The Electricity at Work Regulations say no person shall be engaged in work where technical knowledge or experience is needed to prevent danger unless they have it, or are properly supervised (regulation 16).
The agency's checks help. They don't replace yours. Give every new engineer a short supervised start on your kit, whoever pays their wages.
Temp to perm: read the contract first
Sometimes you book an agency engineer and they turn out to be exactly who you need. Hiring them permanently is common. It can also cost you a transfer fee.
The Conduct Regulations limit when an agency can charge that fee. The fee term can't be enforced unless the contract also gives you the option of a longer hire period instead of paying it. And the agency can't charge it at all if the engineer starts with you after the later of two dates: 8 weeks* after they last worked for you through the agency, or 14 weeks* from their first day with you (regulation 10).
So read the agency terms before the first shift, not when you're about to make an offer. Our post on temp to perm goes through how to handle it fairly for everyone.
If you're thinking of using a self-employed contractor rather than an agency engineer, the rules are different again. Look at IR35 for hirers first.
What we'd do
Here's our view. For a gap that won't close, recruit, and use agency cover to keep the site safe while you do. For a gap with an end date, use cover and don't over-think it.
For the gap you can't size, set a review date. Book cover for eight weeks. At week eight, look again. If the work is still there and still growing, start recruiting before the 12-week rule kicks in.
And price the risk of doing nothing. An empty post doesn't save money if the line stops and nobody can fix it. Put your cost of an hour of downtime next to the agency rate and the decision usually gets easier.
What to do on Monday
- Write down how long you expect the gap to last, and what would change that.
- Read your agency's terms for transfer fees and the extended hire option.
- Put a review date in the diary for any cover booked without an end date.
- Write a proper skills spec for the role, so the agency and the job advert both ask for the same thing.
* The 12-week qualifying period and the 8-week and 14-week transfer fee periods correct as of 6 September 2026. Check GOV.UK on agency workers and the Conduct Regulations for the latest.