Three companies have been found guilty of a fraud which cost Royal Mail at least £70 million over a decade.

Millions of pounds were pocketed in the fraud, which involved the under-declaration of mail that was posted through a network of logistics companies in Buckinghamshire and Berkshire.

A week into the trial at London’s Southwark Crown Court Judge Philip Bartle KC told the jury there had been a “significant development” and the companies involved had now changed their pleas to a charge of conspiracy to commit fraud by false representation.

On Tuesday one representative from Tiger International Logistics Ltd, Worldwide Transport Express Ltd and Global Express Worldwide Ltd each pleaded guilty on behalf of the companies to the conspiracy, which lasted between May 2008 and May 2017.

Members of the jury, although it has happened very quickly, what it means is that this trial has come to an end

The judge directed the jury to find the companies guilty of the charge which states they had “dishonestly” intended to make a “gain for themselves or another” by knowingly processing “untrue or misleading” declarations about the quantity, weight, class and destination of mailings.

The jury, under the direction of the judge, also found Balginder Sandhu, 46, of Slough, Berkshire, and Lakhwinder Sekhon, 42, of Isleworth, west London, not guilty of conspiracy to commit fraud by false representation.

Parmjeet Sandhu, 56, of Slough, pleaded guilty to a charge of obtaining services dishonestly.

The judge told the jury: “Members of the jury, although it has happened very quickly, what it means is that this trial has come to an end.

“In one sense you may find it frustrating because you have heard the opening but heard no evidence in this case but it is the duty of all counsel to try to strive to achieve an outcome which is in the interests of justice.

“I am sure what happened this morning is in the interest of justice. I am sure that this is a satisfactory outcome.”

Narinder Sandhu, who is Parmjeet Sandhu’s brother and owner of Packpost International Ltd, had been described in the prosecution’s opening of the case as the “architect” of the fraud.

Prosecutor Ellis Sareen had said Narinder Sandhu lived with his family at Hadley Grange, a “multimillion-pound mansion” near Beaconsfield, Buckinghamshire.

He also had a Bentley, a Rolls-Royce and a pool house.

Sandhu’s declared taxable income was about £1 million per year towards the end of the period that the fraud was running.

His brother Parmjeet did not become as wealthy, but still made “a lot of money”.

Mr Sareen told the court that “thousands” of items were under-declared by manipulating docket spreadsheets.

Narinder Sandhu and Packpost International Ltd have previously pleaded guilty to the conspiracy.

Parmjeet Sandhu was released on conditional bail ahead of sentencing for all of the offences which is to be set at a hearing at the same court in October.