I am living in belgium and dd (4) is at the local school and doing quite well now with her nederlands. I have been trying to learn a little, by myself at home, but on top of the general difficulty of that ds has been a nightmare sleeper so never had the time and concentration together. Where we are neither me nor dh can get to language classes with 2 small children.
I really don't know how people can stay long term in places and not learn the languages - how, practically, do they cope? Belgium is very xenophobic right now and public services in flanders will only communicate with you in dutch. We've been here 2.5 years. I know of someone in Austria who's been there for nearly 10 years and still not learned German. He seems to find jobs through expat connections. We don't have those, and at the level we look at (not head-hunted, just ordinary low-level professionals) you don't find many job openings that don't require the native language.
I was always learning languages at school; I seemed to have a knack for it but without the budget or background for travel my French now is barely at 'can get by' stage, and the rest of it forgotten.
And there may be part of your answer. If you are not going to travel outside UK except on holiday (I know people who have never been able to afford that ) you don't need other languages, and I haven't noticed active curiosity about other places being a big part of British psyche. Or anywhere else's for that matter. As for holidays, well English is everybody's 2nd language, so you can get by with just that.
Expat life has proved the necessity for languages to us, as it's a pain not having the dutch here and I'd really rather have tried moving to Germany but neither of us speak german.