Plans for a Holocaust memorial next to Parliament would create a "trophy site" for terrorists, the former independent reviewer of terror laws has warned.
The memorial has been proposed for Victoria Tower Gardens on Millbank.
But a planning inquiry has been told by Lord Carlile that the landmark would be a "self-evident terrorism risk".
The Ministry for Housing, Communities and Local Government (MHCLG) said it was confident the site would be secure.
The plan was previously rejected by Westminster City Council, but the final decision will be made by the government following the public inquiry.
However, the plans have significant support from more than 170 MPs and peers, including Housing and Communities Secretary Robert Jenrick.
And last week, Labour leader Sir Keir Starmer told the Jewish Chronicle the memorial was "vital" in order to educate future generations about the Holocaust.
An online planning inquiry into the plans began on Tuesday.
In his written evidence to the inquiry, Lord Carlile said: "From my extensive experience of observing, analysing and discussing terrorism issues with front-line practitioners, I have absolutely no doubt that the proposed site raises a clear - indeed self-evident - terrorism risk.
"I give this warning with regret, but with total conviction. This would be a threat to the public, and also a potential threat to Parliament."
The project features 23 large bronze fin structures and an underground learning centre.
It was announced in 2016 by then Prime Minister David Cameron, who said it would be dedicated to the six million Jewish men, women and children and other victims murdered by the Nazis.
However, several senior Jewish figures have also voiced their opposition to the location of the memorial, while the Royal Parks said it would have a "significant harmful impact" on the area.
Lord Carlile QC said the issue was personal to him.
"I have a strong interest in this," he told the BBC.
"Many of my close relatives were exterminated in the Holocaust. My half-sister's mother was murdered in Auschwitz.
"I am absolutely determined that this should be remembered properly. I just feel that this isn't the right place for it."
He added: "I know - indeed I believe everybody knows - that the Houses of Parliament are an iconic target for terrorists.
"This site is cheek by jowl with the Houses of Parliament.
"This site would also be, potentially, a target for right-wing extremists. It seems to be foolish for these two iconic places to be on the same broad site."
He added: "International terrorists usually want to make a splash. Having a site which combines the Houses of Parliament and the new British Holocaust memorial seems to me to be asking for trouble."
A spokesman for the MHCLG said: "We are fully aware of the security implications associated with this site and we have been advised on measures to mitigate risks.
"The memorial will stand as a reminder to all in parliament, and the whole nation, of our responsibility to remain vigilant against intolerance and bigotry."
In addition to Lord Carlile's security concerns, a group of 42 Holocaust academics raised concerns that the centre would portray Britain as "the ultimate saviour of the Jews".
In a joint letter to the inquiry led by Dr Hannah Holtschneider of the University of Edinburgh, they said: "Situating the UK Holocaust memorial next to the Houses of Parliament is likely to create a celebratory narrative of the British government's responses to the Jewish catastrophe during the Nazi era and beyond."
The project has government backing as well as support from the opposition benches.
Sir Keir told the Jewish Chronicle: "The fight against intolerance and prejudice in our society, and the stain of anti-Semitism, goes on.
"So I offer my wholehearted support to the Holocaust Memorial and Learning Centre and its placement next to the heart of our democracy."
Communities Secretary Mr Jenrick said in February the government remained "implacably committed" to the construction of the memorial.
He said it would ensure "future generations never forget".
Karen Pollock, chief executive of the Holocaust Educational Trust, said the project was important to preserve the stories of survivors of the Holocaust as well as the stories of the six million "whose voices we will never hear".
The works are being led by the UK Holocaust Memorial Foundation.