OttiliaVonBCup said ^When you live and work somewhere you should not pick and choose what bits of the language you use.
Also, it's a vicious circle - you'll never be fluent if you insist on using your first language^
So do you think people who move to the UK should stop using their mother tongue? Not speak it to their children?
No wonder the UK is so far behind most of the rest of the world with modern foreign language learning if this is a prevailing attitudes - other languages are just not valued.
I speak English to my children 100% of the time and we live in Germany - they are fully bilingual and most Germans are suprised they also speak another language.
When I (very occasionally) come across the attitude that as we live in Germany I should speak German to my kids, it is only from older, less educated thick, backward, racist people, 99% of people express nothing but jealousy that my kids get the advantage of being bilingual so easily. I wonder which attitude would be the dominant if we moved back to the UK switched to German as a family language to keep them bilingual. 
I really doubt a lot of the posters on here would forgo speaking English socially to other English speakers if they moved to an area with a different community language - just look at a lot of ex-pat communities...