Detectives have made the UK’s largest cryptocurrency seizure worth nearly $249 million during a probe into an international money laundering ring.

It was connected to the seizure last month of cryptocurrencies worth $158 million – the previous record – by the same London force.

The Metropolitan Police dropped to say which currency was seized and how the funds were believed to have been accrued. A woman, 39, has been arrested and bailed in connection with both seizures.

Graham McNulty, a senior police officer at the Metropolitan Police, said: “While cash still remains king in the criminal word, as digital platforms develop we’re increasingly seeing organized criminals using cryptocurrency to launder their dirty money.”

The seizures come amid heightened concerns over an explosion in cybercrime during the Covid-19 pandemic, particularly a form targeting businesses known as ransomware.

Ransomware blocks organisations’ access to vital files until they pay a fee to criminals to unlock them – usually in Bitcoin because of the difficulty in tracing ownership and the money trail.

The scale of the demands have rocketed with companies on the hook for tens of millions of pounds even after negotiating with criminal gangs, according to a former head of the UK’s surveillance agency GCHQ.

Robert Hannigan, who led the agency from 2014 to 2017, told a cybersecurity conference on Tuesday that large companies were prepared to pay up because the cost of disruption far outstripped the cost of the ransom.