A close friend of the Prime Minister has been found dead in mysterious circumstances at Glastonbury Festival.

Senior Tory Christopher Shale was discovered slumped in a portable toilet in a backstage VIP area yesterday morning.

David Cameron said he was “devastated” as he described his constituency chairman as a valued friend and a “big rock” in his life.

Initial suggestions from Michael Eavis that the wealthy businessman’s death could be a “suicide situation” were dismissed by police. Sources said it was believed he suffered a heart attack.

Festival founder Eavis later expressed his “deepest sympathy” as a police probe was launched on 900-acre Worthy Farm.

Mr Shale, a father in his 50s, was staying with his family in a Winnebago surrounded by a host of celebrities and performers.

The death came just hours after he was quoted in the Mail on Sunday bemoaning difficulties his party faces in recruiting new members.

Mr Cameron, the MP for Witney, said he and wife Samantha were great friends of Mr Shale’s.

“Sam and I were devastated to hear the news about Christopher,” the Prime Minister said.

The West Oxfordshire Conservative Association chairman was “a great friend and has been a huge support over the last decade” in the constituency, Mr Cameron added.

“A big rock in my life has suddenly been rolled away,” he said.

Mr Eavis sent his thoughts to family and friends, before adding: “We work very closely with the police, medical and other emergency services to ensure that the festival is as safe as possible for all 177,000 people on the site.”

Inspector Chris Morgan said inquiries into the death were continuing.

He added: “It is only a couple of hours ago – we are still working on establishing a cause of death.”

A police cordon, patrolled by dozens of officers and security guards, was put up near the backstage shower and toilet area.

The camping area where festival production teams and some performers stay was also blocked off.

A host of celebrities were staying in the cordoned-off area. Wayne and Coleen Rooney were understood to have been camping in a nearby luxury RV.

Mr Shale and his relatives were staying near The Times columnist Caitlin Moran.

The writer tweeted: “Woke up to find the man in the Winnebago next to us died. Bit of a grime start to the morning.”

Revellers reacted with shock as they were told the area was “a crime scene”.

Tom Waite, 35, from Cheddar, was among those staying in the VIP area. He said: “It’s just awful for his family.”

Mr Shale was quoted in a Conservative strategy document leaked to the Sunday tabloid.

Referring to Tory party membership, he was reported to have written: “No reason to join. Lots of reasons not to.”

Mr Shale was the chief executive of Oxford Resources Ltd, a cost reduction company based in Chipping Norton, Oxfordshire.

He was previously chief executive of SGL Communications. He is listed on the website of eurosceptic thinktank OpenEurope as a supporter and was a director of the Centre for Policy Studies.

Most revellers carried on partying unaware as sweltering temperatures ensured they could leave waterproofs in their tents.

Security had already been heightened in the VIP area ahead of Beyonce’s headline gig, which brings the curtain down on this year’s event.

Relatives raised the alarm to festival organisers after Mr Shale, 56, went missing overnight, police said later.