Cameron's friend Shale died after speaking to No 10

A Downing Street staffer could have been the last person to speak to Christopher Shale, the senior Tory who was found dead on Sunday morning in a VIP toilet at the Glastonbury festival.

The Daily Mail is reporting that Shale, 55, was contacted on Saturday and warned that a strategy note he had written for the West Oxfordshire Conservative Association, which covers David Cameron's Witney constituency, had been leaked to the Mail on Sunday, which published it yesterday morning.

Gabby Bertin, the prime minister's press secretary, called Shale around mid-day and left a message telling him that the story was coming out.

According to the Mail, Bertin said it was no big deal but cautioned him against speaking to other journalists. Shale spoke to a second Downing Street official, who was also at the festival, who told him to contact Conservative central office - a call he never made.

Shale was also reported to have spoken to David Cameron's constituency agent, Barry Norton, who told the Mail that "Shale said he was enjoying his Glastonbury weekend and... was very happy and positive in what he had to say to me".

Norton also said that there was a history of heart problems in Shale's family, supporting claims by family friends that Shale suffered "a massive heart attack".

In the leaked document, Shale, a close family friend of the prime minister and a key member of the modernising tendency in the Tory party, said that "over the years we [Conservatives] have come across as graceless, voracious, crass, always on the take" and warned that people had "no reason to join. Lots of reasons not to".

It is believed that Shale's body may have lain undiscovered for up to 10 hours in the Portaloo cubicle in the VIP backstage area. Concerned family members who were with him at the 900-acre Worthy Farm site had reported him missing on Saturday.

Police are waiting on toxicology results to determine the exact cause of death, but have already attempted to dispel claims made by festival organiser Michael Eavis that Shale had killed himself. Talking to reporters on site on Sunday morning, Eavis said he had been told the death was a "suicide situation".

A police spokesman said: "The results of the post-mortem combined with the inquiries conducted into the circumstances surrounding the death indicate it is not suspicious. Therefore Avon and Somerset Police are not treating the death as suspicious. Further tests will be conducted to establish the exact cause of death."

Meanwhile, Cameron led tributes to the businessman and director of the Centre for Policy Studies think tank. The PM said: "Sam and I were devastated to hear the news about Christopher." Shale had been "a great friend and a huge support over the last decade. A big rock in my life has suddenly been rolled away." ·