This is the text of an email sent by Head of News, Helen Boaden, to her staff:

Dear All,

We have had some occasions recently of BBC News staff using social networking sites to share with the world their somewhat controversial opinions on matters of public policy and the future of the BBC. Unsurprisingly, these have been picked up by the wider web and used to discredit the BBC and its impartiality. We have Editorial Guidelines which cover the personal use of the internet …which everyone should observe. We also have brains and judgement which I suggest people fully engage before rushing to communicate. Hx