Demand for a seat to watch Tony Blair give evidence to the Iraq inquiry has been so high that a public ballot is to be held to allocate the limited places.

The ballot, similar to ones used for World Cup tickets or Glastonbury, will see a maximum of just 120 people handed the chance to witness the former prime minister deliver evidence in the flesh, meaning thousands of others will be disappointed.

The audience promises to be a tough one for Mr Blair as one-third of the seats will be reserved for the families of soldiers killed during the Iraq campaign.

No exact date has been revealed for his appearance, which will be between 25 January and 5 February.

His six-hour grilling will take place over two sessions.

Separate ballots will be held for each session to maximise the number of people who can see Mr Blair's evidence to Sir John Chilcot's committee in the small 60-seat inquiry room in Westminster's Queen Elizabeth II conference centre.

Mr Blair will give evidence after the inquiry has heard from key members of his former team, including Alastair Campbell, his former head of communications, and Jonathan Powell, his chief of staff.

For those not fortunate enough to be drawn out of the hat, an overspill room will also be set up in the centre giving more members of the public the chance to watch Mr Blair on a live video link.

His testimony will also be broadcast live on the Iraq inquiry's website.

"There has been considerable interest from members of the public wanting to know how to get a seat for this particular hearing," Sir John said.

"Given the potential demand, we recognise the importance of providing people with certainty about whether or not they will be able to get into the hearings, particularly those who need to travel long distances. We believe the fairest way to do this is to allocate seats by ballot."

The ballot will take place on 18 January and will be carried out independently.

Application forms for those wanting a ticket can be downloaded from the inquiry's website and must be returned by 15 January.

The inquiry heard yesterday that Mr Blair was phoning British representatives in Iraq almost daily after the invasion.

Sir William Patey, Britain's ambassador to Baghdad from 2005 to 2006, said it was the first time he had received instructions directly from the Prime Minister.

"The politics here demanded instant results," Mr Patey said.