Threats to MPs are at "unprecedented" levels, Metropolitan Police Commissioner Cressida Dick has said.
The Met chief disclosed that the number of crimes reported by MPs more than doubled in 2018 from 151 to 342 and was on course to rise further this year.
Assistant Commissioner Neil Basu told a parliamentary committee Brexit was a "huge driver" behind the increase.
Women and people from ethnic minorities were being disproportionately targeted, Ms Dick added.
So far this year MPs and staff have already reported 152 crimes and over 600 incidents while incidents involving MPs are now 126% higher than in 2015.
Appearing before the Joint Committee on Human Rights, Ms Dick said the murder of Labour MP Jo Cox in 2016 had contributed to an "extraordinary set of circumstances" with a level of harassment and abuse not seen before.
"Polarised opinion" on political and social issues was also having "a big impact on the scale and impact of protest activity", she added.
Also giving evidence to the committee's inquiry into democracy and free speech, Mr Basu said Brexit was a driving force behind many of the reports this year.
He said crimes reported to police were "evenly split", with 43% targeted against those in favour of leaving the EU and 47% aimed at people who want the UK to remain.
Ministers have said they intend to pass a law creating a specific new electoral offence of intimidating parliamentary candidates and party campaigners during the run-up to an election.
The government says the offence has been developed to crack down on intimidating or abusive behaviour, which is, in extreme cases, already punishable with a custodial sentence.
Harriet Harman, the Labour MP who chairs the committee, expressed concerns that police officers were not doing enough to protect MPs going about their business.
She raised the example of Anna Soubry, the former Conservative MP who now represents Change UK, who was repeatedly heckled and called a Nazi by pro-Brexit protesters during a media interview outside Parliament in January.
She was then briefly prevented from entering the Palace of Westminster afterwards.
Ms Harman said she felt "uncomfortable" that there were police officers on duty nearby during the incident who did not step in to disperse the crowd.
The commissioner said the Met took its role of protecting MPs "very seriously", and accepted that the Met's presence outside Parliament during that period had been "too passive" but had since been "stepped up".
"It is absolutely not acceptable for parliamentarians - MPs and beyond - to feel intimidated in the work place - that's a given.
"We recognise the increasing concern about protests outside - we have a particular job to prevent crime and disorder, protect property and lives, uphold the law, and ensure people's rights are balanced."