Interesting observations. As one raised in Nigeria, there is no way I wouldn't teach my kids their mothertongue. I have every intention of raisig them in a 2-parent Yoruba-speaking household, hence my wifey would have to be a fluent Yoruba speaker. I think most UK based Nigerian parents from the late 1940s to the early 1990s chose not to teach their kids the mothertongue. Check out the link to the ff article written by A US based Nigerian on the same subject. ( Although it is talks about Naijas in America, the article can be applied to British based Nigerians as well!). Here's the link: http://www.gamji.com/NEWS1822.htm

Enjoy.