AV explainer: How voting change is like the Oscars

What do the Oscars and the upcoming referendum on changing the voting system have in common?

Well, you may not know it but, while most of the Academy awards are decided by a majority vote, one category - that of Best Picture - is chosen with a method which is very like the alternative vote.

The BBC's political correspondent Ben Wright explains, with the help of some Hollywood A listers, how the AV system works.