A top military intelligence official has said the discredited dossier on Iraq's weapons programme was drawn up "to make the case for war", flatly contradicting persistent claims to the contrary by the Blair government, and in particular by Alastair Campbell, the former prime minister's chief spin doctor.

In hitherto secret evidence to the Chilcot inquiry, Major General Michael Laurie said: "We knew at the time that the purpose of the dossier was precisely to make a case for war, rather than setting out the available intelligence, and that to make the best out of sparse and inconclusive intelligence the wording was developed with care."

His evidence is devastating, as it is the first time such a senior intelligence officer has directly contradicted the then government's claims about the dossier – and, perhaps more significantly, what Tony Blair and Campbell said when it was released seven months before the invasion of Iraq in 2003.

Laurie, who was director general in the Defence Intelligence Staff, responsible for commanding and delivering raw and analysed intelligence, said: "I am writing to comment on the position taken by Alastair Campbell during his evidence to you … when he stated that the purpose of the dossier was not to make a case for war; I and those involved in its production saw it exactly as that, and that was the direction we were given."

He continued: "Alastair Campbell said to the inquiry that the purpose of the dossier was not 'to make a case for war'. I had no doubt at that time this was exactly its purpose and these very words were used."

Laurie said he recalled that the chief of defence intelligence, Air Marshal Sir Joe French, was "frequently inquiring whether we were missing something" and was under pressure. "We could find no evidence of planes, missiles or equipment that related to WMD [weapons of mass destruction], generally concluding that they must have been dismantled, buried or taken abroad. There has probably never been a greater detailed scrutiny of every piece of ground in any country."

The document is one of a number released by the Chilcot inquiry. They include top secret MI6 reports warning of the damage to British interests and the likelihood of terrorist attacks in the UK if it joined the US-led invasion of Iraq.

However, a newly declassified document reveals that Sir Kevin Tebbit, then a top official at the Ministry of Defence, warned the defence secretary, Geoff Hoon, in January 2003 that the US would "feel betrayed by their partner of choice" if Britain did not go along with the invasion.

Despite its concerns, MI6 told ministers before the invasion that toppling Saddam Hussein "remains a prize because it could give new security to oil supplies".

Laurie's memo raises questions about the role of Sir John Scarlett, chairman of the Joint Intelligence Committee, who later became head of MI6.