Tony Blair's former press secretary reveals in his diaries that ex-PM often read the Bible before he took 'really big decisions'

Tony Blair had a "wobble" on the eve of his first bombing mission against Saddam Hussein after a late-night reading of the Bible, Alastair Campbell writes in his diaries serialised in today's Guardian.

In a powerful illustration of the impact of Blair's faith on his actions, Campbell writes that a New Testament story about Herod and John the Baptist prompted prime ministerial jitters hours before the launch of an Anglo-American bombing mission against Iraq in December 1998.

Campbell, who famously dismissed questions about Blair's faith by saying "we don't do God", admits in his diaries that the former prime minister often read the Bible before he took "really big decisions".

"TB was clearly having a bit of a wobble," Campbell writes in Power and the People on 16 December 1998, hours before the launch of bombing raids to punish Saddam for failing to co-operate with UN weapons inspectors. "He [Blair] said he had been reading the Bible last night, as he often did when the really big decisions were on, and he had read something about John the Baptist and Herod which had caused him to rethink, albeit not change his mind."

The disclosure of Blair's nerves ahead of his first military assault against Saddam comes a week before the former PM makes his second appearance before the Chilcot inquiry, which is examining the 2003 invasion of Iraq. Campbell writes in today's extracts that Blair gave an undertaking to Saudi Arabia in April 1998 that Britain "would not threaten the territorial integrity of Iraq".

The latest instalment of Campbell's diaries, serialised in today's Guardian, covers the first two years of the last Labour government. The extracts focus on the two major foreign policy changes of Blair's first term: the bombing of Iraq in late 1998, and the successful removal of Serb forces from Kosovo in the spring of 1999.

Campbell also reveals that:

• Margaret Thatcher told Blair during the Nato bombing mission against Serbia in 1999 that she was "appalled" that the civilian side of Nato – ambassadors based in Brussels – discussed bombing targets.

• Downing Street became so alarmed by the criticism of the Kosovo action by the right that Campbell successfully lobbied two key Thatcher allies – her former foreign affairs adviser Charles Powell and David Hart, her adviser during the miners' strike – for help.

• General Wesley Clark, Nato's supreme allied commander, said the alliance was on the "brink of a disaster" when Campbell was dispatched to Brussels to advise Nato on its communications strategy.

• Excited by the international praise which greeted his landslide victory in 1997, Blair joked with Campbell that it was a pity he was prime minister of such a small country. "It's just a shame Britain is so small, physically," Campbell quotes Blair as saying.