London Mayor Sadiq Khan has voiced his “deep concern” that plans for the Holocaust Memorial next to Parliament may be rejected, as heritage organisations objections to the proposals mount up.

He said the project was "vital" to build the memorial in Victoria Park Gardens because it would be "a national asset and a wonderful addition at the heart of our democracy" next to Westminster Palace.

In a statement on Wednesday, the Mayor said: “The National Holocaust Memorial and Learning Centre will be hugely important to London, and to the whole country.

"It will be a powerful symbol against all forms of hatred and teach our future generations about the fragility of peace, and where hatred and division can lead if left unchecked."

He added: "It will be a fitting tribute to the victims of the Holocaust and a strong voice against all forms of prejudice and hatred in the modern world.”

Mr Khan also said he had “warmly welcomed a letter from 174 cross-party MPs and peers to Westminster Council – the planning authority which will rule on the memorial – that highlights its significance”.

He spoke up after Historic England, the non-departmental public body tasked with protecting England’s historical environment, wrote to Westminster Council, describing its “concerns... on heritage grounds”.

It warned the current proposals would “likely have a serious impact on significant and potentially well preserved archaeological deposits”, and “harm the significance of the registered garden” so as to “fundamentally change its character”.

This comes after ICOMOS [International Council on Monuments and Sites] a body that advises Unesco’s World Heritage Committee, objected, saying the plans “would have a massive visual impact” because it would kill a number of trees in the gardens.

Royals Parks, which manages Victoria Park Gardens, also objected, saying the plans would have "significant harmful impacts" on the park's "character and function".

While MPs and Peers have spoken out in support and opposition to the planned memorial’s location, the Holocaust Educational Trust (HET) and the Holocaust Memorial Day Trust (HMDT) have supported it.

HET Chief Executive Karen Pollock said her organisation welcomed Mr Khan's "unflinching support... for this important memorial".

“We are proud to support the national Holocaust Memorial and Learning Centre, positioned right next to Parliament, at the heart of our democracy,” she said.

But, campaigners from the Save Victoria Tower Gardens group described Historic England's intervention as a “further blow” to the plan.

“How many experts from top organisations will it take before the Government listens? The flaws of packing this large museum into a tiny park will not go away,” said Barbara Weiss, an architect and spokesperson for the campaign.

“It is bizarre that the obvious alternative location of the Imperial War Museum is being ignored when it is keen to host the new Learning Centre.”