Building a national Holocaust memorial in a small central London park risks impacting the green space “irrevocably”, opponents to the plans have argued.

Campaigners gathered outside the Royal Courts of Justice on Tuesday in support of a charity’s legal challenge against the Government over planning permission for a UK Holocaust Memorial and Learning Centre in Victoria Tower Gardens, Westminster.

The London Historic Parks and Gardens Trust, while not against the memorial’s concept, is opposed to its proposed location in the triangular Grade II-listed park by the River Thames.

Campaigners have previously raised concerns over the alleged impact plans might have on local trees, potential flooding, and heritage monuments.

Speaking outside the court ahead of the hearing, Louise Hyams, a member of Westminster City Council representing the St James’s ward, which includes the park, said the Imperial War Museum in south London was the “most sensible place” for a new memorial.

“To lose this local park will be a tragedy,” she said.

Ms Hyams said there was “no question” the memorial would affect the park “enormously”, adding: “We’re totally on the side of all the residents [and] everybody who comes to Westminster to enjoy this peaceful space.”

She said the memorial could attract visitors “in their hordes” who would “change the atmosphere in this very peaceful park irrevocably.”

Clare Annamalai, a spokeswoman for the Save Victoria Tower Gardens campaign, highlighted objections over an alleged “flood risk” and a “risk to trees” posed by the plans.

She asked what the proposals would say about “the rights of other green spaces to be protected” if “you can build on that space which is a Grade II heritage park with listed monuments”.

Ms Annamalai said the plans would turn the park “into a civic space rather than a community space”.

She said: “Large areas of the park will no longer be accessible in the same way that they are now.

“How do you behave as a family… in a park that contains a Holocaust memorial? Would it be appropriate to play frisbee or have a boozy picnic?”

Ms Annamalai said it was not “reasonable” or “fair” to expect opponents to provide “fully fledged” alternative schemes, but noted the Imperial War Museum in the neighbouring borough of Lambeth had a “fantastic” Holocaust exhibition.

“The Government should have consulted properly at the start,” she added. “They should have been transparent in their decision-making.

“It’s really for the Government to go back to the drawing board.”

Father Philip Chester, vicar at St Matthew’s Westminster, said the plans had been “hastily” conceived.

He highlighted a “rise in antisemitism” and “rise in intolerance in society”, saying the past should be remembered.

But he said history is “too important” to be “squashed” into a memorial in the park.

He said there is “confusion” over the plans and it is “not clear what the education centre is going to do”.

The Government, which is resisting the High Court challenge, has previously said the free-to-enter memorial would be a “national focal point to honour the six million Jewish men, women and children who were murdered in the Holocaust, and other victims of Nazi persecution, including the Roma, gay and disabled people”.

It said the learning centre will be a “world-class facility” that will give visitors “powerful and engaging experiences to learn about the Holocaust and subsequent genocides through a variety of mediums”.