Image copyright @Montie Image caption Conservative commentator Tim Montgomerie joined in the satire of the debate by sharing this picture

It was the men who did not participate in the Thursday night BBC election debate who dominated the conversation on social media.

When Ed Miliband issued a challenge to David Cameron at the end of last night's event ("Debate me one-to-one") it was already a familiar line on social media, where the challenge had been issued hours before. Earlier in the evening, Miliband had tweeted: "David Cameron has decided not to attend tonight's debate. If you're applying for the job of PM, you should turn up to the job interview." The message was shared more than 8,000 times.

Cameron and Nick Clegg were not included in the debate, after much wrangling over the rules. The emphasis on David Cameron's non-attendance was clearly part of an orchestrated Labour strategy online. Trade union accounts released doctored photographs which accused the Conservative leader of being "too chicken" to take part. Pictures of chickens were widely shared by Labour supporters and they managed to get hashtags like #WheresDave used thousands of times.

Image copyright Tim Roache

"Why is David Cameron not at the debate?" was also a most searched Google term. Even some Conservative commentators joined in the humour by sharing doctored memes of Clegg and Cameron hanging out elsewhere. But many Conservative candidates also rushed to Cameron's defence: "Ed Miliband is wrong. David Cameron was not invited to the challengers debate," tweeted Sam Gyimah.

Image copyright Nick Clegg Image caption Nick Clegg's team tweeted a picture of him enjoying a pint in a pub to show that he was focusing on the campaign trail.

Clegg, who similarly wasn't part of the debate, defended himself online. A picture of him having a pint in the pub was shared on his Twitter account.

"For clarity, I was not invited to [the] BBC debate. I would have happily taken part and proudly defended our strong Lib Dems record in government," Clegg also tweeted as the debate got under way. This was shared over 1,700 times and became the most-shared comment on Twitter during the debate.

Group Hug

After the debate, an image of the leaders of the SNP, the Greens and Plaid Cymru hugging as Miliband watched was shared several hundred times, as commentators highlighted the friendship between the "progressive alliance."

"Miliband under attack from three left-wing women," BBC presenter Andrew Neil wryly commented early in the debate, and his remarks were widely shared online.

A second photo of the three women finishing their hug and going to shake hands with Miliband has quickly been turned into a meme by UKIP. Nigel Farage's account tweeted the image with the words "When they say, 'we're all in this together' they really mean it." That image along with similar versions were re-tweeted more than 800 times.

Image copyright Nigel Farage

"Oh Please!"

Miliband's facial expressions during the debate were also the subject of much discussion online. One picture which some claimed was a reaction shot showing the Labour leader listening to Farage speak about immigration was shared more than 2,700 times and quickly became a meme. (People read Miliband's expression as being an "oh please!" moment).

Farage's suggestion that the audience was not a fair reflection of all the political parties and viewpoints taking part in the general election, and chairman David Dimbleby's swift putdown, became one of the most popular Vines of the evening. This exchange, uploaded by a BBC journalist, was looped 7,000 times in 20 minutes and generated 125 tweets a minute during the live programme.

Farage's comments about money "going over Hadrian's wall" [from England to Scotland] also inspired many comments, as voters in both Scotland and England rushed to point out that the famous monument is actually miles away from the current border between the two countries.

Image copyright Callum Farmer

Miliband v Sturgeon

The tense exchanges between the SNP and Labour leaders were for many the headline of the night. The prospect of them working together in a new Parliament was quickly seized on by opponents. On Facebook, the Conservative Mayor of London Boris Johnson released an instantly popular meme of Sturgeon arguing with Miliband, liked by more than 1,700 people and shared 250 times. The phrase "coalition of chaos" was also used by the Conservative Party's official Twitter and Facebook accounts, and a poster showing the similarities between Sturgeon and Miliband on Facebook was liked by 1,700 people.

Image copyright Facebook/Boris Johnson

The most mentioned leader in the debate was Miliband, followed by Sturgeon, according to Twitter data. The #BBCdebate hashtag was used more than 400,000 times on the night - making it the top trending topic of the night not just in the UK, but around the world.

Reporting by Hannah Henderson, Mukul Devichand and Ravin Sampat

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