Home Secretary Yvette Cooper has lashed out at trans activists who defaced several monuments, including some dedicated to feminist heroes.
Police launched an investigation into what was described as an "emergency demonstration" by protesters after seven statues were vandalised in Parliament Square on Saturday.
The Metropolitan Police said the statues were daubed with graffiti during the demonstration, which was held in response to a Supreme Court ruling on the definition of a woman.
No arrests have been made in connection with the criminal damage, but officers are appealing for witnesses to come forward.
Yvette Cooper branded the vandalism 'disgraceful'
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Photos from the protest showed the phrase "f*g rights" and a heart painted on the banner held by suffragette Millicent Fawcett's statue.
"Trans rights are human rights" was sprayed on the pedestal bearing a memorial to South African military leader Jan Christian Smuts.
Parliament Square is home to 12 statues of political figures, including Winston Churchill, Abraham Lincoln and Mahatma Gandhi.
Plans are underway to remove the graffiti, but specialist equipment will need to be brought in, the Metropolitan Police said.
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Graffiti left on statues in Parliament Square, London
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Campaigners held a rally organised by trans rights groups, trade unions, and community organisations
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In response to the damage, the Home Secretary condemned the vandalism, calling it "disgraceful".
"Criminal damage like this, including to statues of men and women who fought for freedom and justice like Winston Churchill, Nelson Mandela and Millicent Fawcett, is disgraceful - it is right the police are investigating," she said.
"We are strengthening the law to better respect and protect important memorials."
She added: "Freedom of speech and protest are important in our democracy, but this kind of criminal damage is completely unacceptable."
The protest was in response to a landmark Supreme Court ruling delivered on Wednesday that confirmed the terms "woman" and "sex" in the 2010 Equality Act "refer to a biological woman and biological sex".
Trans activists marching in London
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Trans activists protesting agasint the Supreme Court ruling
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The ruling means transgender women with a gender recognition certificate could potentially be excluded from single-sex spaces if deemed "proportionate".
Activists at the demonstration demanded "trans liberation" and "trans rights now", with many waving flags and holding banners as they marched towards St James's Park.
The ruling sparked controversy among various groups, with transgender activists expressing outrage.
Chief Superintendent Stuart Bell, who led the policing operation, said: "Criminal damage and vandalism like this has no place on the streets of London and spoils the area for locals and those visiting."
Graffiti left on a statue of Viscount Palmerston in Parliament Square
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"While the police support the public's right to protest, criminality like this is senseless and unacceptable. We are pursuing this and will take action against those responsible."
The Met is urging anyone with information to call 101, quoting reference 01/7396927/25.
Officers are currently reviewing CCTV footage from the surrounding area.
Police are also dealing with complaints about signs and images reportedly displayed at the protest that were shared on social media.
The Met said their investigation has found that these images and signs are either from historic events, did not take place in London, or do not constitute a criminal offence.
Available footage of the protest is being reviewed and action will be taken if signs displayed breach the law.
