Well isn't that interesting...
www.guardian.co.uk/politics/2012/jun/17/michael-gove-national-curriculum
BTW Annobel, there is lots about writing in different registers already in place in the curriculum.
I think one of the problems is that some people see the teaching of writing as the teaching of grammar, punctuation and spelling in a series of decontextualized chunks, which you then put together. I believe that the systematic teaching of those things is very important, but that writing is a craft and you learn to write by writing.
It is a bit like learning to drive, you can't do the theory first and then do it all smoothly first time, you have to practise, make mistakes and have someone to help you learn from your mistakes. When you write for different audiences you learn the genre. There is a strong tradition of this in the teaching of writing, dating back at least to the National Writing Project in the eighties.