I don't know UK labor law, but I do know that when I worked in finance in the U.S., people were not expecting to take 25 days off per year.

"The company only granted 25 days off per year to UK employees in Namely"

What else do you think employers should be allowed to put in the work contracts and then not provide? Did you expect the agreed salary? Seriously, how is what you expected working somewhere else in any way relevant if the contract says otherwise?