On May 5, a referendum on what voting system the country should use will take place alongside the local council elections.

The national referendum will ask whether the existing first-past-the-post system for electing MPs to Westminster should be replaced with a method known as the alternative vote (AV).

Under first-past-the-post, where you put an X on your ballot paper beside the name of the person you want to vote for, a Parliamentary candidate needs only to win more votes than any other candidate to be elected.

MPs are frequently elected with only 30 per cent of the votes cast, simply because they garnered more votes than anyone else.

Under the alternative vote or AV system, voters rank candidates in order of preference, with a 1,2, 3 and so on.

Candidates must get the support of at least 50 per cent of voters in their constituency to be elected.

If no candidate can manage this on first-preference votes alone, second, third and even later preferences are taken into account until one of the candidates passes the magical 50 per cent mark.

With the referendum fast approaching, Yes and No campaigns are now underway to persuade voters of the merits of each system.

It is the first national referendum the UK has held in more than 30 years.