The law isn’t worth the paper it’s written on, and I think you’ll find that almost all employers have similar policies.
Where I work it’s standard for employees to lose holiday regardless of whether they’ve been off. The reason for that is that staff are able to purchase additional holiday, so many do, and book it all up before others get the chance to even book in their statutory entitlement, meaning that some staff end up with one or two weeks extra holiday so 6/7 weeks off while others aren’t even able to take their actual holiday. It’s a nightmare.
I’ve been off sick since January and I’m about to start my phased return. I haven’t had any annual leave apart from a week I booked off at the beginning of the year for the end of the year iyswim. I’ve been told that the AL calendar is now fully booked, other than the day we’ll be allowed to book off over Christmas, and that I’ll be entitled to carry over five days which isn’t negotiable.
Have spoken to the union (IME unions are generally useless anyway) who have said that they’ve had similar come through from other employees, but due to staff shortages and not knowing what the future holds, carrying over holiday isn’t being permitted.
And there’s literally nothing you can do about it, it’s all very well quoting the law, but taking legal action against your employer A, is costly, and B, isn’t going to build a good relationship between you and them going forward, and when you’ve had a considerable period of absence, even if it is entirely understandable, new employers aren’t exactly going to be looking to employ someone who’s been off for nine months and has then taken their employer to court.
So in my case I’ve just cut my losses.