Axing BBC Four to boost youth television will deprive the elderly and vulnerable who rely on the arts and culture channel, a TV historian has warned. The channel is under threat of being closed or filled with repeats as speculation grows that the broadcaster plans to plough money into programmes for younger viewers. BBC Four, which most nights has fewer than a million viewers with an average age in their sixties, faces having the plug pulled just as the over-75s prepare to lose their free TV licences in August.