Rishi Sunak has railed against “extremist forces trying to tear us apart” during a Downing Street address to the nation.
The prime minister said there has been a “shocking increase in extremist disruption and criminality” and added that “now our democracy itself is a target”.
He described the Rochdale by-election result on Thursday night as “beyond alarming”, and claimed “our streets have been hijacked by small groups who are hostile to our values”.
The announcement comes after the victory of maverick politician George Galloway in Rochdale, following a campaign dominated by the highly-emotive issue of Gaza and dogged by accusations of abuse and intimidation.
Politics latest: Starmer reacts to Rochdale defeat
With community tensions in the UK heightened against the backdrop of the Israel-Hamas conflict, MPs have also spoken of their experiences of receiving death threats and their concerns for the safety of their families after the government announced an extra £31m to protect elected representatives.
The new security package will enhance police protection and help fund private security guards for those facing a higher risk.
In addition, it will ensure all elected politicians and candidates have a dedicated named police contact to liaise with on security matters.
At the same time, Mr Sunak warned the UK was descending into “mob rule” as he told police they must use the powers they have or risk losing public confidence in the face of ongoing pro-Palestinian protests.
It followed chaotic scenes in Westminster last week over the vote on a ceasefire in Gaza.
Commons Speaker Sir Lindsay Hoyle broke with precedent in his handling of the proceedings because he had concerns about the intimidation suffered by some parliamentarians and wanted to give MPs the widest possible range of options for the vote.
But the backlash to his actions, which spared Sir Keir Starmer from the prospect of a damaging revolt by MPs demanding a ceasefire, has left his own position in jeopardy, with dozens of MPs backing a motion of no confidence.