David Lammy, the foreign secretary, claimed he was bringing the “golden age of money laundering” to an end as he announced UK financial sanctions against three high-profile alleged kleptocrats and their key enablers.

On Thursday, the Foreign Office (FCDO) announced sanctions including asset freezes and travel bans on Dmitry Firtash, a Ukrainian billionaire, Isabel dos Santos, the daughter of Angola’s former president, and Aivars Lembergs, a Latvian oligarch.

The UK has long faced criticism from anti-corruption campaigners for an unquestioning attitude towards foreign investors. That approach came under particular scrutiny after Russia’s full-scale invasion of Ukraine, when the UK government under the Conservatives belatedly sought to freeze assets belonging to alleged allies of Vladimir Putin.

Lammy said the tide was turning on corruption after a long period when the previous government allowed the role of London as a money laundering capital to continue.

Susan Hawley, the executive director of Spotlight on Corruption, a campaign group, said: “Today’s bold sanctions send a welcome message that the UK is stepping up efforts to end impunity for corruption and the UK’s role in enabling and harbouring dirty money.”

The FCDO said Firtash had allegedly extracted hundreds of millions of pounds from Ukraine, and is alleged to have hidden millions in the UK property market. Firtash, who previously worked with Russia’s gas producer Gazprom, has already been placed under sanctions in other jurisdictions.

The UK also put his wife, Lada Firtash, under sanctions. The government said she had profited from his corruption and holds UK assets on his behalf, including the site of the old Brompton Road tube station. The government also imposed sanctions on Denis Gorbunenko, a UK-based financial fixer who is alleged to have enabled and facilitated Firtash’s corruption.

Dos Santos is accused of abusing her positions at state-run companies to embezzle at least £350m. Dos Santos was once called “Africa’s richest woman”. She has been subject to an Interpol red notice since November 2022 and last month lost a case at the court of appeal regarding her worldwide asset freeze.

Lembergs, one of Latvia’s richest people, allegedly abused his political position to commit bribery and launder money. He was jailed last year by a court in Riga, Latvia.

Lammy said: “These unscrupulous individuals selfishly deprive their fellow citizens of much-needed funding for education, healthcare and infrastructure – for their own enrichment. The tide is turning. The golden age of money laundering is over.”

Dos Santos told the Guardian that “the decision was wrong, unfair and unjustified” and added that it was part of a “politically motivated campaign of persecution against me and my family”.

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She denied misappropriating any money, and said: “No court of law has ever found me guilty of corruption or bribery. On the contrary, the court in Portugal found in my favour, and ruled that [the Angolan] regime allegations of misappropriation of funds from [the state-owned oil company] Sonangol were not true.”

“The UK government did not review any of these documents and information,” she added.

Firtash did not immediately respond to requests for comment. Lembergs did not immediately respond to a request for comment via his former political party.