The BBC’s Laura Kuenssberg reported late last night:
A senior MP has told me Iain Duncan Smith initially resisted attempts by the Treasury to impose this latest round of cuts to Personal Independence Payments (PIP).
Having agreed them he was then angered when Number 10 tried to force his department to defend the cuts yesterday.
Then today it was signalled that the reforms might be dumped altogether – he concluded that he could not stay in government.
There has been animosity between the chancellor and Iain Duncan Smith for some time.
Eurosceptic MPs believe that Number 10 will try to portray his resignation as part of the EU referendum debate within the party but they deny that it is at all related and point to unhappiness at the DWP building over a period of months.
I understand that David Cameron personally tried to persuade Iain Duncan Smith to stay on.