Ryan Shorthouse, director of Conservative thinktank Bright Blue, said: “It was perfectly reasonable and justifiable to narrow the gap in the contributions made by the self-employed and employees to the public purse and added that any spare resources should be devoted to Britain’s poorest families.

“The finances of the lowest earners in this country – whom the prime minister has described as ‘just about managing’ – are being hit by the the ongoing and deep cuts to in-work benefits in this parliament, introduced by the last chancellor. The focus of government should be softening these cuts, not reversing the class 4 NICS rise.”