Whitehall mandarins launched an extraordinary 13-month effort to block the Iraq inquiry from publishing explosive memos between Tony Blair and George Bush, it emerged last night.

Cabinet Secretary Sir Jeremy Heywood’s attempts to keep the correspondence secret led to a major stand-off with Iraq inquiry chief Sir John Chilcot — and pushed back the publication of his report by a year.

Astonishingly, Sir John admitted he still did not know when the inquiry – which has already cost £9million – would finally be published, five-and-a-half years after it was launched.’

Read more: My struggle with Sir Cover-Up and the mandarins of Whitehall over Iraq report, by Iraq inquiry's £790-A-DAY chairman Sir John Chilcot