A candidate sacked after causing outrage on Twitter, a major row between Gordon Brown and big business and a cameo appearance from Michael Caine. Who said politics was dull?

The starting pistol on this year's General Election was fired on Tuesday, when the Queen flew over to Buckingham Palace from Windsor Castle in a helicopter to meet the Prime Minister.

She agreed to his request to end this Parliament, and the leaders of the three main parties were on the road within minutes of Brown's visit to the palace.

They headed into marginal constituencies for heavily-staged photo opportunities – but it was Brown's comments over business opposition to his planned National Insurance rise that became the first big issue of the campaign.

He claimed businessmen had been deceived when they backed the Tories' plans not to increase it.

Many responded, in a spiky Alan Sugar-style, by saying they were not the type of people who could be duped by politicians.

On Thursday, Michael Caine – star of Zulu and Get Carter – sprinkled some celebrity on the campaign as he sat alongside David Cameron at his morning press conference.

He was backing a new plan for a form of national service for 16-year-olds.

Under the two-month voluntary scheme, teenagers will spend a week away from their homes bonding with children from different backgrounds, with problem teenagers urged to sign up by youth clubs and schools.

Yesterday, social media claimed its first scalp.

Stuart MacLennan, the Labour candidate for Moray in Scotland, resigned after posting a series of offensive remarks on Twitter.

He is the first Twitter casualty, but it is unlikely to be the last agenda-setting story to break from either Facebook or Twitter.

There are still four weeks to go, the polls are still tight and few political pundits are ready to call it either way.

The odds on a hung Parliament, where no party has a working majority, shorten by the day, as the tightest election race for decades continues.