It’s a bittersweet victory for Scottish Prison Service (SPS) backroom staff who have won a hard-fought battle for equal pay.

Frontline prison officers – the majority men – have been getting hefty bonuses for three years but non-operational workers – the majority women – got nothing.

Trade union PCS has now forced the prison service to give backroom staff a backdated payment of £4,000 – but only to those earning more than £18,871.

That means the lowest-paid prison staff have been overlooked, prompting PCS to threaten the prison service with industrial action.

The problem centres on the prison service pay structure. The lowest-paid prison officer earns more than £18,871 and the equal pay claim was pegged to prison officers’ salaries.

So, anyone performing a back-office function and earning a salary less than the lowest-paid prison officer gets nothing.

That means people in low-paid jobs in finance, administration, maintenance and human resources will miss out.

Meanwhile, some colleagues who earn as much as £36,000 a year get an additional £4,000 in their August pay packet.

It’s clear that these workers should get this money, which was paid to prison officers on similar salaries over the last three years.

Of course, the prison service could have extended the payout to the lowest-paid non-operational staff but chose not to.

They could now have another fight on their hands. PCS is preparing a new campaign to ensure the lowest-paid get the £4,000 bonus.

And that campaign could see a consultative ballot held of strike action, which could cripple the prison service’s back office functions.

In 2018, it shouldn’t need a union to threaten strike action so that low-paid workers are treated fairly.

It would make sense for the prison service to see off the threat now and hand the lowest-paid the extra money they – of all staff – deserve.