Labour activists last week began rallying behind the hashtag #WeAreCorbyn to fight against what they claimed were "smears" against Jeremy Corbyn's name.

The hashtag quickly created a Twitterstorm spreading globally and claiming the top spot in the UK Twitter trends chart. Soon after, #ResignWatson began trending. The party's deputy leader, Tom Watson, faced demands to quit after challenging Corbyn's handling of the antisemitism row.

Watson claimed Labour should use the International Holocaust Remembrance Alliance definition of anti-Semitism - something Corbyn refused to do.

But despite the massive uptake of #WeareCorbyn and #ResignWatson, focusing on the sheer numbers of tweets in the "hashtag politics" ignores a fundamental question: Do they really work?

Measuring the offline impact of a social media campaign is a tricky subject, said Alex Krasodomski-Jones, a researcher at think tank Demos. “It's one of the more difficult things that we get asked to do,” he added.