A 25-year-old is arrested on suspicion of harassment by officers investigating Twitter abuse aimed at feminist campaigner Caroline Criado Perez and Walthamstow MP Stella Creasy.
Both women have complained about being sent vicious tweets on the site in the past week.
A Scotland Yard spokesman said: “Today, 30 July, Northumbria Police arrested a 25-year-old man on suspicion of harassment.
“This arrest will form part of two ongoing MPS investigations relating to allegations made to police by two separate victims, who made reports of malicious communication to police on 25 and 29 July.”
Ms Criado Perez, 29, has said Twitter needs to “get a grip” on security, as it emerged bosses were likely to face a grilling from MPs.
She said the social network was ill-equipped to handle episodes of sustained abuse and needed to work more closely with police to deal with internet trolls.
Ms Criado Perez met Twitter directors last night along with Ms Creasy, who received a similar torrent of abusive messages after she offered support to the freelance journalist.
“This will have been a wake-up call for Twitter,” Ms Criado Perez said.
“It will hopefully have led them to realise that they are not equipped to deal with this kind of thing properly.
“They need to get a grip and figure it out.”
The campaigner, who received assurances that Twitter is working to improve its procedures for reporting menacing behaviour, said the police also needed to “step up”.
“We had a positive conversation about making reporting quicker, simpler and more focused on getting results for the victim,” she added.
“I feel that finally they’re taking this issue seriously, though it’s a shame it’s taken this worldwide outcry for them to act.
“We’ll be keeping up the pressure in the coming weeks, but the signs of some serious, positive changes are good.”
On Sunday a 21-year-old was also arrested in the Greater Manchester area on suspicion of harassment offences.
Twitter bosses look set to face questions from MPs when the Culture, Media and Sport Committee examines issues surrounding child protection in the Autumn.
However Del Harvey, head of trust and safety at Twitter, said the internet giants “does have policies against a lot of harassment”.
She added: “A threat of rape or violence is not something that’s protected by that sort of concept of anything goes.”
Ms Harvey told Channel 4 News: “There is sometimes a perception that Twitter is the Wild West [of the internet] and that there are no rules, there are rules.
“It’s a balance between making it really easy to report content but then also preventing others from trying to silence people, who maybe they just don’t agree with.”