An aide to Nigel Farage is facing blackmail and money laundering charges in the United States after being arrested at Chicago’s O’Hare airport as he tried to travel back to Britain with the former Ukip leader.

George Cottrell allegedly agreed to launder money for undercover agents who were posing as drug traffickers and is facing 21 counts relating to money laundering, fraud, blackmail and extortion,.

An Arizona federal indictment said that in 2014 Cottrell agreed to launder their purported drug proceeds by transferring it to offshore accounts and later met them in Las Vegas, arranging for them to transfer $20,000 (£15,500) to an associate.

He was arrested on 22 July at O’Hare airport as he attempted to return to the UK with Farage after they visited the Republican party convention in Cleveland.

Cottrell, who is in his 20s, also tried blackmail the fake drug traffickers by threatening to report them to the police unless they paid him 130 Bitcoin, then worth around $80,000 dollars, according to the indictment.

A Ukip spokesman said: “George was an unpaid and enthusiastic volunteer for the party over the period of the referendum.

“We are unaware of the details of the allegations excepting that they date from a time before he was directly involved in the party.”

Cottrell, who has been denied bail by a judge who said he “poses a serious risk of flight” comes from an aristocratic family. His uncle is Lord Hesketh, a former hereditary peer, who worked for former prime minister Margaret Thatcher before losing his seat in the Lords in 1999 as a result of the House of Lords Act. He later defected to Ukip. Cottrell’s mother, Fiona Cottrell, is the daughter of another peer.