Mr Sunak promised “further announcements”, but warned: “There are genuine practical and principled reasons why it is incredibly complicated to design.”
He added that there were “genuine questions about practicality, fairness and delivery, which is why it requires careful thought”.
The delay was revealed as the Prospect union warned that “freelancers are crying out for help”, as their livelihoods disappeared.
“They need it today so they can pay their bills at the end of the week. If they can’t, the whole economy suffers,” said Mike Clancy, its general secretary.
Bectu, the union for freelancers in the media and entertainment sectors, said the government’s existing offer would be worth just £4,800 a year to its members – when normal average earnings were £38,000.
Mel Stride, the Conservative chairman of the Commons Treasury committee, revealed it had been flooded with pleas for help, after launching an inquiry.
“We have received over 14,000 responses, mostly on issues relating to self-employment, from people who work in a wide variety of professions, including childminders, taxi drivers and hairdressers, he warned.
“We need some urgent action for this sizeable group of workers, at least nearly a million zero hour workers – maybe at least another million more.”