Favoured by the likes of Sir Elton John, Hugh Grant and Rod Stewart, the hotel’s staff were surprised to see a “J Prescott” booked into one of its £5,000-a-night suites last year during a property conference in the French town.

News of the British guest quickly reached several UK newspapers, who jumped to the conclusion that the deputy prime minister was living it up at the taxpayers’ expense. John Prescott denied the reports that followed and, until now, the matter has remained a mystery.

However, last week The Sunday Times established that a member of the Prescott family was indeed a guest at the hotel during the annual Mipim property conference in the south of France in March 2005. It was Johnathan Prescott, the deputy prime minister’s oldest son, whose party occupied the opulent suite. His father was staying at a cheaper hotel down the road.

The conference, which brings together the “big hitters” of the British property industry, marked the arrival of Prescott Jr as a player in Britain’s lucrative property business.

In retrospect, it also illustrates the potential for the men’s paths and interests to cross, with father and son pressing the flesh of many of the same businessmen at the lavish event.

It is not known if Prescott’s permanent secretary was made aware of Prescott Jr’s presence at the conference or indeed whether she was made aware of his career in property at all. Certainly there is nothing declared in the Commons register.

This weekend the Conservatives are pushing for urgent answers to these and other questions. Their inquiries, which seek to shine a light on a series of deals Prescott Jr has been involved in since launching his property business at the conference last year, could pose a serious threat to his father’s already precarious political position.

In particular they will be asking whether the deputy prime minister knew that his son was involved in the purchase of the Eaglescliffe Logistics Centre, a former industrial site near Middlesbrough that is now being considered by central government for housing development.

This is crucial as the Office of the Deputy Prime Minister was directly involved in assessing the need for housing in the area — something that would pose a clear conflict of interest for Prescott Sr.

Exactly a month before the Riviera conference, Prescott Jr had set up a business with Richard Carlowe, a property developer from north London. Carlowe had recently left his position as “bid manager” at William Pears Group, where he specialised in bidding for contracts involving the public sector.

According to his entry on the website for alumni of his old school, Carlowe was “heading a team shortlisted to buy all of the empty hospitals in England (4,500 acres)”. He says he has now abandoned this plan.

Prescott and Carlowe founded Estate Partnerships — a firm jointly owned by the pair — and announced their arrival on the scene with the trip to Cannes. Prescott’s room was organised by an unidentified property developer.

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