Sir John Chilcot, chairman of the long-delayed report into the Iraq War, has worked just 16 hours at the Inquiry's headquarters over the last two weeks, it has been reported.

The retired civil servant is said to have spent just five half-days at his Westminster office in the last fortnight - despite his inquiry running five years behind schedule.

More than £10million has been spent on the official inquiry into the war since it was set up in 2009 with the aim to be completed by the end of 2010, but a publication date has still not yet been given.

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Half days: Sir John Chilcot, pictured, chairman of the long-delayed report into the Iraq War

But Sir John, who claims up to £790-a-day, was spotted at his office on only five of the last 10 working days, spending a maximum of four hours inside, according to the Sun on Sunday.

It comes just days after David Cameron told Sir John to name the date he will deliver his report for the sake of the families of those who died in Iraq.

The Prime Minister gave the ultimatum after the grieving mother of one of the British servicemen killed told him how desperately they want answers.

Whitehall officials want the retired civil servant to present a timetable for publication after Parliament returns in October following the party conferences.

Mr Cameron said he was stepping up his demands after he met a mother whose son was killed near Basra as he attended a ceremony at the National Memorial Arboretum in Staffordshire in June.

'Losing patience': Prime Minister David Cameron

He said: ‘I want to see it as soon as possible. Right now I want a timetable.

‘More important than anything is thinking of the parents who lost loved ones in Iraq.

‘The most powerful conversation I’ve had about this was with a mother who said to me at the Staffordshire Arboretum, when we were commemorating the Bastion Memorial Wall for Afghanistan, it’s the parents and the families who want answers.

‘For their sake, as well as for the sake of the public, we’ve got to get on with this.

‘I can’t make it go faster because it’s a public inquiry and it’s independent, but I do want a timetable and I think we deserve one pretty soon.’

In June, Mr Cameron wrote to Sir John to warn he is ‘fast losing patience’ with the Inquiry amid claims the report might not appear for yet another year.

In letters between Sir John and the Prime Minister, the chairman said could not yet give a timetable for publication.

He said responses submitted by individuals and organisations who have been criticised in what is called the ‘Maxwellisation process’ have ‘opened up new issues’, while others have not yet replied.

Sir John wrote: ‘It is now essential that all remaining responses are received so that the process can be completed.

‘Only when all responses are in our possession and have been evaluated will I be able to write to you with a realistic timetable for completion.’

He added: ‘I and my colleagues understand your concern that it has not been possible to publish our conclusions before now. I am sure you will also share my desire to ensure that those conclusions – covering a period of nine years – hold firm once published.’

In the exchange, Mr Cameron went on to say he had instructed the Cabinet Secretary Sir John Heywood to meet with Sir John to discuss how the civil service could help speed up the progress of the Inquiry.

War: A British soldier attempts to escape a burning tank after an incident in the Iraqi city of Basra in 2005

But last month it emerged that Sir John had turned down the offer of extra resources. MPs called for Sir John to stop being paid after it emerged he and his team have shared more than £1.5million in fees.

Sir John is paid £790-a-day, while the three other committee members, Sir Lawrence Freedman, Sir Roderic Lyne, and Baroness Usha Prashar, get a £565 daily rate.

In the past year alone, £119,300 has been pocketed by the committee and its two advisers, General Sir Roger Wheeler and Dame Rosalyn Higgins.

Since the inquiry was set up six years ago, they have received more than £1.5million, an average of £231,308 each.

A further £892,400 was spent last year on the wages of the 11 civil servants and three support staff who make up the Inquiry’s secretariat.