Trying to track down Twitter trolls behind rape threats

A 21-year-old man has been arrested after a feminist campaigner was deluged on Twitter with abuse and threats of rape, Scotland Yard has confirmed. Caroline Criado-Perez faced abuse after successfully campaigning for a woman's face to appear on UK banknotes.

Twitter responded by saying it was testing ways to introduce a button for reporting abuse with every Tweet. But amid a storm of protest Twitter's own response has been branded weak and inadequate.

Newsnight's Paul Mason has been on a troll hunt to see if he can track down any of the individuals behind the abuse.