Speaking moments after Mr Corbyn finished his flagship conference speech, Mr Rotheram described how he looks forward to working with the left-wing party leader.
Joked that he and Corbyn would “kill with kindness” supporters of Tony Blair who have yet to reconcile themselves to the new Labour leader.
Mr McDonnell’s blueprint won a wary reaction from business, with the CBI warning that an active monetary policy could fuel inflation and drive up interest rates, while the British Chambers of Commerce said Labour “must not confuse supporting growth with state control over the economy”.
Corbyn said his party rejects the government’s assertion there is no alternative to more cuts in public services, educational support and the National Health Service. “I think the era when we could just do down the workforce because they haven’t got anywhere else to go is long gone”.
Those with leftish political leanings believe that governments are wise to run deficits much of the time. But it said a thriving private sector is a necessary component to generate the wealth needed to achieve Corbyn’s objectives.
For sure, the Tory conference will be as stage-managed as it’s possible for any party conference to be, but whatever triumphalist speeches come from the podium, the European Union issue will be simmering away at fringe meetings and in hotel bars.
Mr Corbyn told the audience: “Let us put our values, the people’s values, back into politics”.
“It’s not prepared to learn the lesson that the Italian Government could have quite easily have taught them – that you can intervene”.
“I said a few pretty blunt things about the way people are living in very poor quality housing”. “You don’t win elections on a mantra of misery”, he said.
McDonnell spared Miliband from personal criticism of why Labour lost the election – it failed to establish economic message which would have allowed the party to become a clear anti-austerity party.
“I think David Cameron’s idea of being the One Nation Conservative Prime Minister will be thrown out by such a move”. We don’t at the moment, what we have is a government that is cutting tax credits for the very poorest and most vulnerable.
But the prospect of rifts in a party where many – not least among its MPs – do not share all of Corbyn’s left-leaning priorities hung over the occasion.
Divisions at the top level of the party could be exposed later as the conference in Brighton discusses its policy on extending airstrikes against Islamic State. “They are aspirational. They want to feel good about life”, he said.
He said: “It’s busy and it’s demanding and it’s pressurised and it’s exciting and it’s challenging – and I’m loving every minute of it”.