The death of the nurse Jacintha Saldanha has put the business of hoax calls under the spotlight. Where is the line between humour and cruelty?

Hoax calls - where someone winds up a friend or colleague by pretending to be their boss or an important person - are almost as old as the telephone itself.

They have been a staple of TV and radio entertainment programmes since the 1950s when American comedians Steve Allen and Johnny Carson began making them on the Tonight show.

There are numerous examples of rich and powerful people being hoaxed. The Queen in 1995 spent 17 minutes talking to a man she thought was the prime minister of Canada. It was actually Pierre Brassard, a Canadian radio presenter and impressionist.