IDS has bolstered those who decry '˜cruel Tory cuts'

He has been such a longstanding eurosceptic that he was one of the Maastricht rebels in the 1990s who could have brought down John Major’s government.

Mr Duncan Smith, known as IDS, was not then in the cabinet so he was not one of the people that the prime minister of the time was referring to in his famous “bastards” remark, but he was an associate of them.

IDS was in fact too far to the right to be a successful Tory leader after his elevation to that post in 2001 and was ditched two years later before he even fought a general election.

Ideology, however, was not his only failing. IDS was thought to lack the leadership qualities.

Now he has dramatically quit David Cameron’s cabinet with a blistering attack on the government bid to “balance the books on the vulnerable”. This is an extraordinary assault.

That IDS is such a strong supporter of Brexit means it is hard to escape the sense that the timing of his departure and onslaught has been chosen to inflict maximum damage on the prime minister and the man who was until recently considered his likely successor, George Osborne, the chancellor.

That duo are the helm of the EU Remain campaign.

Mr Duncan Smith’s complaint is not entirely without merit. The Conservatives will soon implement an inheritance tax that is inappropriate at this time, but popular with the public.

But he has inflicted grave harm on a key plank of the government’s programme: welfare reform.

Welfare in the UK has spiralled far beyond anything the founders of the welfare state envisaged. Given the scale of the national debt and the public insistence that health and education must be ring-fenced, it had to be reformed and cut.

IDS has greatly emboldened the Labour claim of cruel Tory cuts and will make further reform difficult. If his legacy is continuing extreme UK indebtedness, it will be a sorry one.