George Osborne: ‘It’s not different from what previous chancellors have done, Labour and Conservative.’ Photograph: Christopher Furlong/Getty Images

George Osborne has defended earning £320,000 in five speeches since being sacked as chancellor in July, saying he is behaving no differently from his predecessors.

In an interview with the Guardian in Liverpool about his plans to close the north-south divide by continuing to build his “northern powerhouse” from the backbenches, Osborne said he did not think people hit by austerity measures would consider his extra-curricular earnings unfair.

“When I left No 11 unemployment had never been lower in the north, there were more people in work here, incomes were rising, the country was obviously not in crisis any more economically,” he claimed.

Osborne was replaced by Philip Hammond, once his deputy as shadow chancellor, who has since ditched his predecessor’s economic targets and accepted that the deficit would grow, rather than fall, in the light of the UK’s vote to leave the European Union.

When the Hammonds moved into Downing Street, Osborne signed up with Tony Blair’s US agency, the Washington Speakers Bureau, and embarked on a summer speaking tour.

The most lucrative engagements were two events for the investment bank JP Morgan, for which he received £81,174 and £60,578, a speech for Palmex Derivatives (£80,240), and another for the Securities Industry and Financial Markets Association (£69,992).

He said on Friday: “As a member of parliament I disclose all my earnings. These are relatively new rules. I think it’s quite right that people can see what I do and what I am paid and so on. It’s not different from what previous chancellors have done, Labour and Conservative. The difference is that it’s disclosed. And I think that’s a positive step forward.”

None of his constituents in Tatton, Cheshire, had challenged him on his non-parliamentary earnings, he added.

Osborne’s biography on the bureau’s website says he “oversaw major reforms: the regeneration of the north of England through the northern powerhouse; forging a new relationship with China; and an overhaul of the UK pension and welfare systems”.

Speaking before a meeting in Liverpool of his new business-led thinktank, the Northern Powerhouse Partnership (NPP), Osborne acknowledged the project was still in its infancy. “It’s early days but there is real excitement in the north and if I can sustain it through the partnership I have created, through the meetings we have been having, through my voice in the House of Commons, that’s a good thing. As chancellor of the exchequer – here we are in a great maritime city – I was able to launch the ship down the slipway, if you like.”

Launching the NPP in September, Osborne told the BBC that Theresa May had had “a wobble” over whether to continue with the northern powerhouse idea. But he now insists that his successor is dedicated to the project, pointing to Hammond’s northern powerhouse strategy published with last month’s autumn statement.

“If the northern powerhouse depends on one chancellor of the exchequer being in office, or one government being in office, it is not going to endure,” he said. “The reason I created the Northern Powerhouse Partnership and chose this – of all the various things I could have done with my political energy on leaving office – was because it’s got to be owned in the north, it’s got to be sustained in the north of England, it’s got to be able to endure changes of administration.”

It was not frustrating having to invent a thinktank to lobby the government when he had so recently controlled the nation’s finances, Osborne insisted. “One of the things you learn is there are lots of ways to shape the debate about how our country is run. And of course if you are sitting in No 11 Downing Street you are a very powerful figure in that debate. But you can also shape the debate in the way I think I can, as a backbench MP, by creating this partnership with local Labour leaders in Liverpool, Sheffield, Manchester and the like, and with big businesses such as Unilever.”

Osborne said he was still trying to understand why so much of the north of England wanted to leave the EU – though not his own constituency, he stressed, which narrowly voted 51.2% to stay. But he said that people in the smaller, industrial towns and city outskirts may have felt left out as the city centres boomed.

He said: “I think one of the big challenges we have got ahead is that there has been an amazing revival in these city centres in the north over the last 20 years but the industrial towns in between and the suburbs have felt, I think, a bit left behind. There have been a lot of good government initiatives from all governments to revive the waterfront, to rebuild the docks, but go a bit further out from the city and people I think feel that they haven’t seen enough of the economic growth of the country.”

He added: “We are leaving the EU and the challenge now is to make sure that in the economic cost we pay for that the price is not paid by some of the poorest people who feel already that the system is not working for them.”

The former chancellor suggested that the deal May had offered to Nissan, which persuaded the Japanese car manufacturer to stay in Sunderland and build two new models there, should be extended to every business.

He said: “If the government was saying to Nissan, ‘we want to make sure we have the freest possible trade with the EU with no tariffs and no obstacles’ and it was on the basis that Nissan stayed then we should be offering that deal to the entire British economy, not just to Nissan.”