The BBC is clamping down on freelance columns and books written by its news and current affairs journalists in a bid to maintain its impartiality, reports Broadcast.

BBC correspondents and freelance news and current affairs presenters will be banned from any off-air activities, including media training, if they are seen to "undermine the BBC's reputation for impartiality".

The corporation updated its editorial guidelines on impartiality in May. Prior to that, restrictions were originally tightened in January 2004 following the David Kelly affair.

BBC staff who have book deals must get permission from departments heads, and can only write about subjects that will not "compromise their on-air role".