Britain, like many countries, has became a multicultural society and many citizens don't have English as their first language. Also, English is becoming the main world language, and for many years has been the principal second language in non-English speaking countries.
It's also important that indigenous English speakers learn to use their native language correctly to express themselves and their thoughts clearly. Some may even become writers or teachers.
Language is a very valuable human gift and needs to be treasured and cultivated. It's vital to communication between human beings. Think how different the world would have been if such intimate communication had not been possible: no books, no poetry, no written history, no literary works, no lyrics to accompany music, limited technological development, etc.
From nationwide surveys it's become increasingly clear that there is still an unacceptably high level of illiteracy in the community which has to be addressed through better education. Many foreigners have remarked that English has evolved into a very rich language while many other languages do not have this degree of richness. Perhaps this is because the English language has over time incorporated influences and derivations from other languages. Let's treasure our language!