A National Crime Agency (NCA) attempt to seize mansions in Hampstead and Highgate belonging to the daughter and grandson of a former Kazakh president under so-called “McMafia laws” has been thwarted in the High Court.

A mansion on the Bishop’s Avenue – which is known colloquially as “Billionaire’s Row” and connects East Finchley to the Heath – is among three which the NCA sought possession of last May using unexplained wealth orders (UWO), as is another multi-million pound home in Denewood Road, near to Highgate Golf Club.

The third property is an apartment in Chelsea.

The Bishop’s Avenue high-security mansion is occupied by Nurali Aliyev, grandson of former Kazakh leader Nursultan Nazarbayev, with the Highgate property connected to his mum Dariga Nazarbayeva.

Mr Aliyev and Ms Nazarbayeva challenged the orders, which were introduced in 2018 as part of the “McMafia laws” - named after the BBC organised crime drama and the book which inspired it.

The NCA argued the properties were bought using the money of Rakhat Aliyev, formerly a senior member of the Kazakh government who died in an Austrian prison in 2015 while awaiting trial on two charges of murder.

Nurali Aliyev is Rakhat Aliyev’s son and Ms Nazarbayeva his ex-wife.

Giving judgment remotely on Wednesday, Mrs Justice Lang overturned all three UWOs, ruling that “the NCA’s assumption” that Rakhat Aliyev was the source of the funds to purchase the three properties was “unreliable”.

The judge said there was “cogent evidence” that Dr Nazarbayeva and Nurali Aliyev had founded the companies which owned the properties and provided the funds to purchase them.

In statements, both Mr Aliyev and Dr Nazarbayeva welcomed the judgement and slammed the NCA investigation. Mr Aliyev said the NCA had even made “shocking slurs against me, my family and my country.”

The NCA’s Graeme Biggar said the agency would be appealing the ruling. He added: “The NCA is tenacious. We have been very clear that we will use all the legislation at our disposal to pursue suspected illicit finance and we will continue to do so.”

Duncan Hames, director of policy at campaign group Transparency International UK, said the ruling was “a setback” for the NCA, but described the decision to appeal against the judgment as “encouraging”.