British police said Tuesday they were investigating violent and sexually explicit Twitter postings directed at a lawmaker in a growing row over threats to women on the social network.

Stella Creasy, an MP with the opposition Labour party, faced a stream of abuse after supporting a feminist activist who was targeted for campaigning for an image of novelist Jane Austen to appear on banknotes.

Another lawmaker said she too was receiving a barrage of offensive messages, while a man has been arrested and bailed over rape threats to feminist campaigner Caroline Criado-Perez.

“This isn’t about Twitter, this is about hatred of women and hatred of women who speak up,” Creasy told BBC radio on Monday.

“Twitter needs to be explicit that sexual violence and sexual aggression will not be tolerated as part of their user terms and conditions.”

High-profile women in Britain have long complained of online harassment but the issue reached front pages after Criado-Perez said she received “about 50 abusive tweets an hour for about 12 hours” last week.

Scotland Yard said Tuesday that police had received an allegation from an MP about “malicious communications” over comments on Twitter.

Creasy re-tweeted a series of tweets that included threats from accounts named “killcreasynow” and “eatcreasynow,” which have now been suspended.

Creasy said she was reporting the abuse to both Twitter and police.

Lawmaker Claire Perry, from Prime Minister David Cameron’s Conservative Party, likewise re-tweeted a string of message including threats of sexual violence and one that read, “please disappear into obscurity and/or alcoholism. Or die, whatever.”

“I am tempted to shut down my Twitter account given the trolling going on incl. To me — but that would be giving in,” Perry tweeted.

Perry has been advising Cameron on his plans to introduce an “opt-in” system for blocking Internet pornography.

The abuse to Criado-Perez sparked a huge outcry among Twitter users and prompted more than 60,000 people to sign an online petition demanding the network introduce a “report abuse” button and review its rules on abusive behaviour.

Twitter has introduced a report button on tweets in its iPhone app and plans to bring it to other platforms.

But some users say the form to which it links is too complex and time-consuming for those receiving a barrage of abusive tweets.

In a blogpost titled “We Hear You,” Twitter said on Monday: “We are not blind to the reality that there will always be people using Twitter in ways that are abusive and may harm others.”

Del Harvey, senior director for trust and safety, wrote that manual reviewing of all tweets was not possible as 400 million of the 140-character messages are sent each day around the world.

But it said it used both automated and manual systems to assess reports of users violating its rules, which bar “direct, specific threats of violence against others.”

Police on Sunday arrested a 21-year-old man on suspicion of sending malicious communications to Criado-Perez, whose banknote campaign culminated Wednesday in the announcement Jane Austen would feature on the £10 note from 2017.

The Bank of England had previously announced changes that would have left Queen Elizabeth II as the only woman represented.