Within a day of launching, the appeal on the CrowdJustice website had reached its target of £50,000.

The lawyers estimated they need £150,000 to get to the point of bringing proceedings against Mr Blair, given the huge costs of launching a complex High Court legal action.

The fundraising website states: “Those responsible should be held to account. Now it is down to us, the Families, to ensure that justice is done. Not only for the sake of our children, siblings, parents and spouses, whose lives we can never get back, but to deter our state officials from ever again abusing their positions with such tragic and far-reaching consequences.”

The families have resorted to bringing their own case because the International Criminal Court has ruled out bringing proceedings against Mr Blair while the Crown Prosecution Service has twice rejected calls for him to face criminal prosecution in the UK.

The taxpayer has already paid the costs of ex-ministers and officials, thought to include Mr Blair, for legal advice ahead of publication of Chilcot earlier this month. The prospect of Mr Blair’s defence being paid for will appal his detractors.

He is reckoned to have earned tens of millions of pounds since leaving Downing Street in 2007 through a consultancy and investment business often operating in countries where he established contacts as prime minister.