Illness: Tory peer Lord Ashcroft has suffered a ‘life-threatening’ illness over the past fortnight

Lord Ashcroft, author of the explosive biography of David Cameron, suffered a life-threatening illness a day after the book was serialised, it emerged last night.

The ex-Tory deputy chairman had to be airlifted to hospital and was in intensive care for 18 days suffering from septic shock.

Lord Ashcroft had been visiting war graves and battlefields in Turkey to mark the centenary of the First World War Gallipoli campaign when he was struck down with severe stomach pain.

He was treated with antibiotics, and was able to fly to the Turks and Caicos Islands in the Caribbean. However his condition deteriorated, and he ended up having to be airlifted to a US clinic.

The 69-year-old billionaire’s illness caused major kidney and liver failure, and left him battling for his life.

Last night he missed the official launch of the book Call Me Dave, which was serialised in the Mail last month. The launch was attended by a clutch of senior Tory MPs and ministers. He sent a message which said: ‘I am reliably informed my book has caused a little bit of a stir.’

He went on: ‘I have fought many political and business battles over the past half century but this is the first one – and I trust the last – in which I haven’t led from the front.’

Responding to what he called ‘hysterical, ill-informed’ criticism of the book, which was co-written with award-winning political journalist Isabel Oakeshott, he added: ‘The publication, so soon after the last election, was carefully timed to ensure that whatever our inquiries threw up they caused no harm whatsoever to the chances of the Conservative Party and its leader being re-elected.’.

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Event: The book was co-written by award-winning journalist Isabel Oakeshott (left), who was among the many attendees at the launch at Millbank Tower in London last night - along with Ukip leader Nigel Farage (right)

In attendance: Vicky Pryce (left), ex-wife of disgraced MP Chris Huhne, was also at the event, as well as 'Plebgate' MP Andrew Mitchell and wife Sharon Bennett (right)

The book caused shockwaves throughout Westminster, thanks in part to an allegation about a university initiation ceremony involving a dead pig. It also contained damaging claims about the Prime Minister’s foreign policy.

Lord Ashcroft, who donated more than £8million to the Tory party, claimed in the book that the PM had reneged on the offer of a major job in Government if the Tories won the 2010 election. After the snub, Ashcroft withdrew his financial support for the party.

In the biography, he also alleged that Mr Cameron had not been truthful about when he had learned of the Tory peer’s non-dom status.

Questions continue to dog the Prime Minister about what he knew about Lord Ashcroft’s financial offshore status – which meant he did not pay full UK tax on his overseas assets.

After being serialised in the Mail, the book, which was attacked by allies of Mr Cameron, was officially published at the Tory conference two weeks ago.

Arrivals: Tory MP Alan Duncan (left) was there, along with Stanley Johnson, father of Boris Johnson (right)

PM: The biography of David Cameron (pictured yesterday in the Commons) disclosed Lord Ashcroft's fury at the Prime Minister for going back on a vow to reward his support for the Tories with a top job in government

Observers had pointed out how unusual it was that Lord Ashcroft – who has regularly attended the conference for two decades – was absent. During his speech, the Prime Minister even took a mild swipe at the peer, his former ally.

Not knowing of his illness, Mr Cameron referred to himself as a ‘hooker’ in reference to his favoured rugby position at school. He went on to say: ‘That’s a factual statement. Not a chapter in Ashcroft’s new book.’

It will be a surprise to the Tory establishment that the reason Lord Ashcroft missed the conference was his life-threatening condition, which saw his blood pressure drop to a dangerously low level.