The billionaire arms dealer welcomed by the British establishment

Sudhir Choudhrie and Nick Clegg

Billionaire Sudhir Choudhrie has been welcomed by the British establishment.

His family's Stellar International Art Foundation owns more than 600 rare works of art by artists including Picasso, Renoir and Andy Warhol.

He has been photographed receiving a business award from Theresa May and his family has given more than £1.6m to the Liberal Democrats. The 67-year-old is now an adviser to Lib Dem party leader Tim Farron.

Mr Choudhrie and his family run a global business empire that includes hotels, healthcare and aviation.

But an investigation by BBC Panorama and The Guardian suggests he is also one of the world's biggest arms dealers.

Leaked documents from the Choudhries' Swiss bank show that the family's companies were paid almost 100m euros by Russian arms firms in one 12-month period alone.

One company owned by the Choudhrie family, Belinea Services Ltd, received 39.2m euros between October 2007 and October 2008. Another company, Cottage Consultants Ltd, was paid 32.8m euros in the same period, while a third company - Carter Consultants Inc - was paid 23m euros.

Panorama: How Rolls-Royce Bribed Its Way Around The World is on BBC One at 20.30 and available on the BBC iPlayer afterwards.

The leaked documents say one of the Russian arms firms paying the Choudhries "makes cruise missiles".

Some of the payments were viewed as suspicious at the time by the Swiss bank Clariden Leu. Its compliance office in Singapore raised anti-money laundering alerts and the Choudhrie family accounts were reviewed by the bank's risk management team.

It's not clear what action - if any - the bank eventually took. But the leaked report describes the payments from the arms companies as "incoming funds from clients offset business".

Offset payments are sometimes paid by arms companies to provide investment in the country that is buying the weapons. But anti-corruption campaigners say offset payments can be used as a way of funnelling bribes to middlemen and officials.

Sudhir Choudhrie is also alleged to have acted as a secret middleman for Rolls-Royce

In the leaked documents, Clariden Leu describes the Choudhrie family as being "very wealthy with an overall fortune of approx $2bn".

Sudhir Choudhrie declined to comment, but lawyers acting for Bhanu Choudhrie have said he had no knowledge of the Clariden Leu documents.

"The report to which you refer appears to be a confidential bank document. Mr Choudhrie has not broken any money-laundering rules in any of his business dealings at any stage."

The lawyers said our questions about offset payments by Russian arms companies were too vague.

"You have not given the dates or amounts of the alleged payments or the basis on which you say they were 'suspicious' or made in relation to Russian arms deals. The business of Cottage Consultants was conducted in a lawful and proper manner."

In 2014, Sudhir Choudhrie and his son Bhanu were arrested as part of a Serious Fraud Office investigation into Rolls-Royce. Both were released without charge.