I didn't say I wasn't wrong. I'm barely wrong though. It's clear what I meant unless you're intentionally trying to find fault.
You're nitpicking to score internet points.
They're entitled to the equivalent of 28 days holiday, pro rata - which as you've said is easiest calculated by 5.6 weeks.
No, I'm nitpicking because I've seen enough employees come screaming about their 'rights' and making fools of themselves in the workplace because of bad advice/information given out on the internet about employment law. You stated, without caveats, that
You're entitled to 28 days paid leave a year. The whole calculation they're doing is to work out how much they pay you during that point.
Which is just plain incorrect. You also advised the OP that you thought the way his holiday was being accrued was against the law, which is also incorrect.
The working time directive, which contains the statutory requirements for annual leave, makes absolutely no mention of days whatsoever, it explicitly refers to the entitlement in weeks only. Now, it may seem a small thing, but if someone hadn't been there to clarify the entitlement to the OP, it could have led to unnecessary mistakes or confrontation with his employer for no good reason.
If you're going to give someone advice about their legal entitlements, you have to be spot on about it.