When should a flag be flown at half-mast?

Following the death of King Abdullah flags were lowered on key public buildings in London. But the decision to fly them at half-mast drew sharp criticism from some prominent politicians over abuses of free speech, women's rights and the country's role as cradle of Islamist extremism.

Graham Bartram, Chief Vexillologist at the Flag Institute, a national flag charity, and author of the book British Flags & Emblems told the programme that Saudi Arabia have been flying its flags at full mast.

"Saudi Arabia is about the only country in the world where we could get away with not flying it at half mast because Saudi Arabia doesn't fly its flag at half-mast."