Theresa May will demand that companies like Twitter and Facebook “step up” and tackle online abuse as she warns that aggression is consuming British political debate.
In a speech to mark the centenary of the suffragettes winning the vote for women, Ms May will announce a string of proposals that aim to make social media companies more accountable.
Speaking in Manchester to mark the 100-year milestone, Ms May will set out how online abuse is more often directed at women and minorities.
The Prime Minister will say that the anniversary of the 1918 Representation of the People Act which delivered the vote to women, should make us consider “what values and principles guide our conduct” of political debate.
She will then add: “While there is much to celebrate, I worry that our public debate today is coarsening.
"That for some it is becoming harder to disagree, without also demeaning opposing viewpoints in the process."
Outlining how abuse of political candidates and representatives is often targeted at women, gay people and ethnic minorities, she is expected to add: “In the face of what is a threat to our democracy, I believe that all of us - individuals, governments, and media old and new - must accept our responsibility to help sustain a genuinely pluralist public debate for the future.
"The social media companies themselves must now step up and set out how they will respond."
The Prime Minister will announce plans for a Law Commission review of legislation to ensure that actions which are illegal offline are also illegal online.
And she will pledge to establish a new annual internet safety transparency report, to provide data on how social media companies are dealing with abusive material.
Ms May will endorse the recommendations of a report into intimidation produced last year by the Committee on Standards in Public Life, which called for legislation to shift the balance of liability for illegal content to the social media companies.
A social media code of practice will be released later this year, while the Government will publish its Internet Safety Strategy in the spring.
Reflecting on the centenary Ms May is expected to say: "As the woman at the head of our country's government, a century after my grandmothers were first given the right to vote, my mission is clear.
"To build that better future for all our people, a country that works for everyone, and a democracy where every voice is heard."
She will later address a reception in Parliament to launch a year-long Vote 100 programme of events to celebrate a century of female suffrage.
All female MPs past and present have been invited, in what is expected to be the largest gathering of the UK's women politicians ever organised.
Labour's shadow cabinet were meeting at the Museum of London, currently home to an exhibition on the suffragettes.
Speaking outside the broom cupboard in the Palace of Westminster where Emily Davison hid overnight on census day in 1911 as part of the suffragette campaign, Labour leader Jeremy Corbyn said: "One hundred years later, the struggle for equality continues.
"There are still too few women in Parliament, women still do not receive equal pay for equal work and many face discrimination in the workplace and in everyday life.
"But the actions of Emily and other campaigners stay with us as we strive to build a truly equal society that works for the many, not the few."
For the first time, the Parliamentary Archives will display four original Acts of Parliament extending the franchise.
These are the 1918 Representation of the People Act itself, the 1918 Parliament (Qualification of Women) Act allowing women to be MPs, the Equal Franchise Act 1928 which gave women the vote on the same terms as men, and the Life Peerages Act 1958 which allowed women to sit in the House of Lords as life peers.
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