Thousands of hours of surveillance footage from the January 6 attack on the US Capitol are being made available to the Fox News host Tucker Carlson, a stunning level of access granted by the House speaker, Kevin McCarthy, that Democrats condemned as a “grave” breach of security.

The hard-right host said his team was spending the week at the Capitol, preparing to reveal their findings.

Granting exclusive access to January 6 security footage to such a deeply partisan figure is a highly unusual move, seen by some critics as essentially outsourcing House oversight to a TV personality who has promoted conspiracy theories about the attack.

“It’s a shocking development that brings in both political concerns but even more importantly, security concerns,” said Dan Goldman, a New York Democrat who was a chief counsel during Donald Trump’s first impeachment trial.

Many critics warned that Capitol security could be endangered if Carlson aired security footage that details how rioters accessed the building and routes lawmakers used to flee to safety. A sharply partisan retelling of the Capitol attack could accelerate a dangerous rewriting of the history of January 6, when Trump encouraged supporters to attempt to overturn Joe Biden’s election.

“It is not lost on anyone that the one person that the speaker decides to give hours and hours of sensitive secret surveillance footage is the person who peddled a bogus documentary trying to debunk responsibility for the January 6 riot from Donald Trump onto others,” Goldman said.

“Kevin McCarthy has turned over the security of the Capitol to Tucker Carlson and that’s a scary thought.”

McCarthy’s office declined to confirm the arrangement, first reported by Axios.

Images and videos from the Capitol attack have been widely circulated by documentarians, news organizations and rioters themselves. But officials have held back much of the surveillance video that offers a detailed view of the grisly scene and brutal beatings of police.

The House committee investigating the January 6 attack worked with US Capitol police to review and release segments of the footage as part of public hearings last year.

The chief of Capitol police, Tom Manger, said only: “When congressional leadership or congressional oversight committees ask for things like this, we must give it to them.”

House Democrats planned to convene on Wednesday for a private call to hear from Bennie Thompson of Mississippi, who chaired the January 6 committee, and others. The House Democratic leader, Hakeem Jeffries, called McCarthy’s decision an “egregious security breach”.

“Unfortunately, the apparent disclosure of sensitive video material is yet another example of the grave threat to the security of the American people represented by the extreme Maga Republican majority,” the New Yorker told House colleagues.

Zoe Lofgren of California, the former chair of the House administration committee and a member of the January 6 panel, said: “It’s really a road map to people who might want to attack the Capitol again. It would be of huge assistance to them.”

Carlson, who produced a documentary suggesting the federal government used the Capitol attack as a pretext to persecute conservatives, confirmed that his team was reviewing the footage.

“We believe we have secured the right to see whatever we want to see,” Carlson said on his show on Monday.

It’s not clear what protocols Carlson and his team are using to view the material, but he said “access is unfettered”.

The January 6 committee, which was disbanded once Republicans took the House, created a secure room for staff to examine more than 14,000 hours of footage. The process took months, according to a person familiar with the investigation.

Any clip the committee wanted to use had to be approved by Capitol police. If police had an objection, the committee would engage in negotiations to redact any content that could potentially endanger the force or its protection of the Capitol.

Capitol police reported an increase in threats to member safety over the last several years. The number of possible threats against members of Congress rose from about 4,000 in 2017 to more than 9,600 in 2021, then declined last year to 7,501.

Republicans said McCarthy’s decision was part of his commitment to create a more transparent House and engage in oversight, as Republicans launch investigations touching many aspects of government.

“I support Speaker McCarthy’s decision,” said Bryan Steil of Wisconsin, the House administration committee chair.

Hard-right figures cheered. “For all of you that doubted we would release the tapes. Here you go!” tweeted Marjorie Taylor Greene of Georgia, now close to McCarthy.

Rodney Davis, a former Illinois Republican, said if the former House speaker Nancy Pelosi’s daughter, the film-maker Alexandra Pelosi, was able to film on January 6 and release her footage, McCarthy should be able to grant Carlson access.

Others said the two situations are not comparable, as countless hours of footage have been released from many sources.

“I think we should remember that the January 6 attack happened in broad daylight,” said Sandeep Prasanna, a former investigative counsel on the January 6 committee.

“My concern is that I don’t see how releasing thousands of hours of footage to one handpicked controversial media figure could ever produce the same factual and careful analysis that the committee produced over that year and a half.”