British police helped to "develop evidence" against Madeleine McCann's parents as they were investigated by Portuguese police as formal suspects in the disappearance of their daughter, the US ambassador to Portugal was told by his British counterpart in September 2007.

The meeting between US ambassador Al Hoffman and the British ambassador, Alexander Wykeham Ellis, took place a fortnight after Kate and Gerry McCann were formally declared arguidos, or suspects, by Portuguese police. The McCanns have said that there was "absolutely no evidence to implicate them in Madeleine's disappearance whatsoever."

In a diplomatic cable marked confidential, the US ambassador reported: "Without delving into the details of the case, Ellis admitted that the British police had developed the current evidence against the McCann parents, and he stressed that authorities from both countries were working co-operatively."

The comments attributed to the ambassador appear to contradict the widespread perception at the time that Portuguese investigators were the driving force behind the treatment of the McCanns as suspects in the case.

The disclosure comes as WikiLeaks founder Julian Assange returns to court in an attempt to secure bail following his arrest last week at the request of Swedish authorities who want to interview him over allegations of sexual assault. A number of other cables released by the whistleblowers' website shed new light on aspects of the financial crisis. Revelations include:

• RBS chairman Sir Philip Hampton said the board of the bank breached their "fiduciary responsibilities" by allowing the takeover of the Dutch bank ABN Amro.

• The Bank of England governor, Mervyn King, was so worried about the health of the banks that he proposed a secret international fund to recapitalise them six months before the collapse of Lehman Brothers.

• US officials expressed doubts in October 2008 over whether Ireland appreciated how much trouble its banks were in.

In one of two cables referring to the McCann case, the US ambassador notes: "Madeleine McCann's disappearance in the south of Portugal in May 2007 has generated international media attention with controversy surrounding the Portuguese-led police investigation and the actions of Madeleine's parents."

He reported that his British counterpart thought "that the media frenzy was to be expected and was acceptable as long as government officials keep their comments behind closed doors".

It was not until 21 July 2008 that the Portuguese authorities shelved their investigation and lifted the arguido status of the McCanns. Responding to the contents of the cable, a spokesman for the McCanns told the Guardian: "This is an entirely historic note that is more than three years old. Subsequently, Kate and Gerry had their arguido status lifted, with the Portuguese authorities making it perfectly clear that there was absolutely no evidence to implicate them in Madeleine's disappearance whatsoever.

"To this day, they continue to work tirelessly on the search for their daughter, co-operating when appropriate with both the Portuguese and British authorities."

British authorities had substantial involvement in the investigation launched after Madeleine disappeared in May 2007 from the holiday apartment where the McCanns had left their three children in bed before joining friends at a nearby restaurant in the Algarve village of Praia da Luz. At least one British sniffer dog was used in the investigation and, according to reports, was said to have picked up the scent of a dead body in the apartment.

In 2008, when a dossier detailing investigations by Portuguese police was made public, it emerged British scientists had warned that DNA tests on a sample from the McCanns' holiday hire car were inconclusive days before they were made suspects. It is known that the Forensic Science Service analysed material sent to Britain by Portuguese police. A spokesman for Leicestershire police said their involvement in the investigation was limited to co-ordinating UK-based inquiries on behalf of the Portuguese authorities.