I can only compare to my native Sweden where it’s completely normal for people to take 3 weeks or even more off in a row. In the UK, even 2 weeks seems to be seen as quite long.
Nevertheless, everywhere I’ve worked in the UK (I’ve been here 11 years), people do tend to use their full allowance, except maybe 5 days which it’s common you are allowed to carry over to the next year at the employer’s discretion. Often, there is a bit of a scramble towards the end of the holiday year when people have a lot of holiday left they need to take or they will lose it. Never plan any important project deliveries around that time!