The comments were made to ITV News Deputy Political Editor Anushka Asthana as part of the Tonight programme Rishi Sunak: Up Close
William Hague has called on Tory rebels to stop the in-fighting, with a chilling warning that if the party goes into opposition, it may never return to government.
The former Tory leader said that while things were "difficult, exhausting, and exasperating" for Rishi Sunak, he was sure the PM would keep calm in response.
"This is a very resilient person who can keep going for a long time under difficult conditions, without panicking, without losing heart, and without losing courage," he told me, in an interview for ITV's Tonight programme.
"And we've seen that already in his premiership. How capable he is of doing that, of keeping going. I think it was meant to be Winston Churchill who said, 'if you are in hell, keep going'. That's the only way out. Don't stand still."
Lord Hague, who has been somewhat of a mentor to Mr Sunak since the younger politician took over as MP for Richmond, in Yorkshire, said he was an excellent prime minister, who was hardworking, focused on detail, honest and had high standards.
But when asked where Mr Sunak might struggle, he admitted that the politics of governing the Tory party was hard.
Party politics 'comes harder to Rishi...' William Hague tells Anushka Asthana
"It's a big shock to be a party leader. Suddenly you're responsible for everybody and everything in the party. And that requires being really good at party politics... [of] thinking of things in a very partisan way, in a very party political way. And that comes harder to Rishi...
"Anybody would find it tough. But I think for, for such a, such an intelligent and rational person, the operation of party politics is a bit harder."
Lord Hague argued that what Mr Sunak inherited made things extremely difficult, saying it was "like taking over an army on the battlefield when it's just been fighting himself... Imagine how difficult it is to straighten out that arm and make sure it marches in the same direction".
He argued that no Conservative PM would be in a better position after inheriting "that battlefield" but admitted things were incredibly difficult for Mr Sunak right now.
'I would say your only chance is to work together,' William Hague tells Anushka Asthana when she asked about disloyal MPs
Asked what his message was to disloyal MPs, Lord Hague said: "I would say your only chance is to work together."
How long could the pain go on for the Conservatives, I asked. "If a party goes into opposition, there's no guarantee of when it will get back or if it will ever get back. When the Liberals went into opposition in the 1920s, they never came back other than as a coalition partner every 30 years or so. There's no guarantee of ever coming back."
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He urged MPs to see this election year as being in the "sales department".
"You're not in the creativity department anymore. You're not in the redesign department, you are in the sales department.
"Conservative MPs need to understand that they've actually got a better story to tell than some of them sometimes give the impression and they've got a really good Prime Minister, and they really ought to be able to sell that. But they all do have to join in selling it.
He said he hoped Mr Sunak and the party would at least make the election competitive, arguing that however much it looked like the Tories would lose, it wasn't a done deal.
"It might turn out that that's just too difficult, that the accumulation of years in office and all the problems the country and the world has experienced in that time will prove too much. That might be true, but it's not definitely true. It's not written in stone or in the stars. We still have a choice at the next election."
He argued that the Tories were in a better position than when he was leader between 1997 and 2001.
Lord Hague described how he was impressed by Mr Sunak from the moment he saw him on stage at a selection for the Richmond seat that he had previously held. He said he knew immediately that Mr Sunak would go far.
I asked about Mr Sunak's somewhat "eager" nature that I saw while we were filming for the Tonight programme. Almost "Tigger-like" I said.
Lord Hague replied: "There's something much more sophisticated and powerful here than Tigger. But nevertheless, I know what you mean by eager."
He described Mr Sunak getting up at 5am to go cow-milking with farmers as a candidate, and still working at 10 at night in the Cabinet room as PM - going through papers.
"He is one of the hardest working individuals I've ever come across in politics and his own personal discipline makes that easier - he doesn't drink and he doesn't eat that much.
"The result is a high energy level all the time. Most people, you know, have a big lunch, slow down a bit in the afternoon, have their big dinner sleep it off. But Rishi his energy level is like this," added Hague raising his hand in the air. "There's no slump. He just keeps going all the time."
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