Will social media help Jeremy Corbyn win Labour leadership - again?

With Jeremy Corbyn's battle to retain the leadership against challenger Owen Smith now firmly under way, the hashtag #JezWeCan has been replaced by #JezWeCanAgain.

Mr Corbyn stole a march on his rivals online when he first ran for leader last year, and judging by the number of people talking about him on social media, he still has the advantage.

Mr Corbyn's personal page has more than 783,000 "likes" on Facebook, while the lesser-known Mr Smith has yet to reach 10,000.

Mr Corbyn's team claims the reach of his official page is 8.5 million people, and many more users will see pro-Corbyn content from other sources, ranging from videos of speeches at rallies to a positive take on Labour's election results to attacks on Owen Smith's background working for drugs giant Pfizer.

For his part, Mr Smith has the support of the majority of Labour MPs and Saving Labour, which campaigns online and is backed by celebrities including JK Rowling.

Avoiding the 'mainstream media'

Underlying much of the social media activity surrounding Mr Corbyn is the assumption that he will not be treated fairly by national newspapers and broadcasters.

At the weekend some supporters began using the Twitter hashtag #WeAreHisMedia to suggest they will do the job of transmitting the Corbyn message instead. It was used 36,500 times during a mass posting organised last Saturday.

David Cameron once said that "Britain and Twitter are not the same thing", but Twitter does have an active UK user base thought to be approaching 15 million.

An anonymous social media post criticising Owen Smith

Facebook has many more - thought to be nearing 30 million - and Mr Corbyn has talked repeatedly about the importance of social media.

"We are getting enormous cut-through on social media and I think sometimes the national debate is framed around the political media circle that often ignores the reality of how many people get their information," he recently told the Guardian.

But most of the pro-Corbyn material on sites such as Facebook and Twitter does not come from Mr Corbyn or his team, as social media expert Carl Miller from the think tank Demos explains.

"It's not a bottom-down process, it's not a co-ordinated campaign from professional digital strategists. It allows organic grassroots movements to spring up and generate an incredible amount of noise," he says.

It's impossible to predict the outcome of this or any other election based on social media activity, says Mr Miller. But, he adds: "What all the activity shows us is how galvanised and excited the core vote really is. [Pro-Corbyn campaign group] Momentum is incredibly active, and always has been much more so than the Labour Party establishment.

"In general what I think this is doing, whether it's Momentum or other movements like UKIP, is it allows anti-establishment surges to happen. That kind of message of radical change always spreads better on social media than the 'let's keep things where they are' message."

Large crowds

These online movements are also increasingly spilling out on to the streets, Mr Miller believes, pointing to the large gathering of supporters at Westminster in June as Jeremy Corbyn was hit by a wave of front-bench resignations.

Momentum, which organised that event, claims a reach of 18 million across all its Facebook pages. "It's extremely important because it helps our offline activities," a spokesman said.

"Lots of people think social media exists in its own separate bubble. It really doesn't - it helps us do things like organise in 24 hours 10,000 people at the Keep Corbyn rally outside Parliament."

Mr Corbyn's team points to large crowds that have gathered in the past week to hear him speak - reportedly as many as 3,000 in Hull, and in Liverpool on Monday where estimates ranged between 5,000 and 10,000.

His supporters online posted pictures of those large crowds with the hashtag #MerseyBunker, a riposte to claims from his critics that Mr Corbyn is stuck in a bunker in London.

Jeremy Corbyn meets supporters at a rally in Liverpool

Some were then mocked for mistakenly posting pictures of even larger crowds gathering to see Liverpool FC celebrating their Champions League victory in 2005.

His critics claim he had agreed to a debate with Mr Smith on Channel 4 News the same evening, and say his ability to draw a large crowd online and at rallies has little bearing on his ability to win elections.

A spokesman for Saving Labour, the group set up to back the challenge to Mr Corbyn, said: "He is not in any sense addressing a wider electorate either within the Labour Party or the country.

"The reflected bubble is causing him to believe he has a social movement out there which will sweep all before it which is just nonsense, as the polls will tell you."

That group, which uses the hashtag #SavingLabour, has been posting pictures of large rallies ahead of the 1983 election in which Michael Foot was badly defeated by Margaret Thatcher.

It claims that it too has been effective online. The spokesman said it sent at least 70,000 people to the Labour Party website to join as registered supporters, giving them a chance to back Mr Smith before the ballot closes on 21 September.

Mr Corbyn has placed a lot of emphasis on the power of social media, but his team is not making any assumptions.

"Support for Jeremy on social media has grown exponentially since the start of the leadership campaign. We hope this will assist in getting our message out," a source said.

It remains to be seen how far he can convert the followers he has amassed on social media into votes, both within the Labour Party and the country at large.

Produced by the BBC's Social and UGC team