Reform UK proposes £100m 'round-the-clock' security plan for MPs
All 650 MPs would be provided with "round-the-clock protection" under a Reform UK government, according to Zia Yusuf.
The policy is estimated to cost up to £100m and resources would be allocated to protect former politicians still active in public life, the party's home affairs spokesman said.
Yusuf said MPs must be able to air their views "without fear" for their lives, with his announcement coming after the death of party spokeswoman Ann Widdecombe.
Counter-terrorism police have said the former Conservative MP was killed in a "targeted attack". Prime Minister Sir Keir Starmer said he was "truly horrified" by Widdecombe's death, adding: "We must do more to defend our democracy."
Speaking in his final Prime Minister's Questions, Sir Keir told the House of Commons: "I've tasked officials across government to identify the best mechanisms for taking this work forward so it can move as quickly as possible."
Sir Keir also suggested installing a memorial shield in the Commons to honour Widdecombe. Similar memorials were installed to honour murdered MPs Jo Cox and Sir David Amess.
Labour MP Andy Burnham, who is due to replace Sir Keir as PM on 20 July, believes a "serious review" is needed into MPs' security.
Figures from the Independent Parliamentary Standards Authority (Ipsa) showed security assistance funding claimed by MPs totalled £4.38m in 2021/22 and £3.88m in 2022/23.
Ipsa said responsibility for security funding passed to the House of Commons in April 2023.
A Commons spokesperson declined to share specific costs relating to security but said "all MPs are offered appropriate security measures".
Sir Keir described Commons Speaker Sir Lindsay Hoyle as "instrumental" in defending the safety of MPs.
Yusuf announced Reform's latest policy during a central London press conference in which he criticised the language used by rival parties about Reform.
He also said Reform leader Nigel Farage "lives his life under the ever-present threat of mortal danger" and those who "question his need for security should stop".
Yusuf told reporters: "Politicians from other parties are perfectly entitled to disagree with our policies and criticise us.
"They're of course free to criticise us. But they must stop equating us to murderous regimes that butchered tens of millions of people and committed some of the greatest horrors in history."
Yusuf also said: "I do not want to see what happened to Ann happen ever again. This has to stop."
He added: "If Reform win the next general election, as home secretary I will ensure all Members of Parliament of all parties are provided with round-the-clock protection.
"We will also allocate significant new resources to protect former politicians still active in public life."
Yusuf said the support for former politicians would be "based on a threat assessment".
The BBC's Alex Forsyth asked Yusuf about language he has used on social media, including calling Sir Keir "sick" and "depraved" and describing the Conservatives as "open border lunatics who deserve their extinction".
He has also accused Labour and Conservative politicians of being "traitors".
Yusuf replied: "If you use the word 'traitor', for example, the definition of 'traitor' is somebody who is engaged in betrayal.
"And as far as I'm concerned it is demonstrable that, for example, the Conservative Party has acted in betrayal of the people who voted for them."
He added there is a "clear difference" when comparing his language to comments he had criticised from other parties.
A House of Commons spokesperson said: "The ability of members and their staff to perform their parliamentary duties safely, both on and off the estate, is fundamental to our democracy."
The spokesperson said any assessment of an individual MP's security arrangements or advice is "subject to a rigorous risk-based assessment, conducted by security professionals and with input from the police and a range of professional authorities".
The spokesperson added: "These are naturally kept under continuous review."