As long as your employer gives you 22.4 days paid holiday per year the law is being complied with.
If he wants, say, to give you just a couple of single days off in a month (with both of those days being in the 'middle' of your working weeks) and then insist that you work on Christmas Day (if that's a day of the week which you'd normally work) at your normal pay rate, then it's all perfectly legal.
i.e. no employee ever has any entitlement to receiving their holiday periods in whole weeks (unless, of course, they've got a contract which makes such a provision). Equally, they've never got any entitlement to take single days off if the employer wants to insist on a 'full weeks only' rule wherever it's practical to apply it.
No holidays in December is a common rule in many workplaces. (The rail company I worked for applied the same rule). There are also still some companies which work to the old idea of 'wakes weeks', where everybody in the company has to take their holidays at the same time (as determined by the employer) simply because the business shuts down during those periods. There are also other jobs where the exact dates of employees holidays are fixed by the employer, with zero flexibility, with teaching being a prime example. (Teachers might get plenty of holidays but they're stuck with paying peak prices if they want to go away anywhere).
So, legally, you've not got a leg to stand on. All you can do is to hope that your employer can be persuaded to show some flexibility, either by you or by your union representative (if relevant).