Protocol of calling an election

Something that not everyone knows is what the procedure is for calling an election. This article does a good job of giving an insight into the arcane world of Parliament:

“When Mr Blair goes to see Her Majesty, she could refuse the dissolution of Parliament and tell him "Labour has a huge majority and if you can't form a Government I'm going to ask that nice Jack Straw to do so instead."

Technically she could, but she won't be inviting the Foreign Secretary and Blackburn MP, or even Chancellor Gordon Brown in for a chat over their future. For the convention is that when the Prime Minister decides to call a General Election, the Queen dutifully agrees.” Link