In reply to mick taylor:
I'm not sure you're correct. The law changed from 20 days min holiday + bank holidays, to 28 min holiday.
In the old system I believe you had pro-rata 20 + whatever bank holidays you were working (or days in lieu). But now you have to include some fraction of bank holidays.
My wife's company does this. Her 3 day week means she is off for more fixed days (bank holidays + other fixed days) than her entitlement and she loses a day from her pro-rata floating days.
Similarly, if you join a company 1st June and leave 1st December you'll only get 1 bank holiday, but you'll be entitled to 14 days min holiday, which they might incorrectly calculate as 10 days.
I think this is why 25 days holiday (ex bank holidays) is becoming a popular condition, it reduces the likelihood of falling foul of the law.