Kemi Badenoch delivered a sobering and uncompromising message to her own party on Saturday within minutes of being elected as its new leader, saying the Conservatives had to become “honest” again if they were to stand any chance of recovering as a political force.

This is the Badenoch way: blunt and straight to the point. The cheers and whooping had hardly died away at the news that she had defeated Robert Jenrick by 53,806 votes to 41,388 votes before she was laying down the law.

“Our party is critical to the success of country,” she said. “But to be heard, we have to be honest. Honest about the fact that we made mistakes. Honest about the fact that we let standards slip. The time has come to tell the truth.”

Whichever individuals she had in mind – Boris Johnson, Liz Truss, Rishi Sunak or whether it was everyone all together – there could be no repeat. It was time “to reset our politics and our thinking”.

For the first three months after July’s election, British politics had been stuck in a pre-budget phoney war. Government ministers had been unsure what money they would have to spend so couldn’t talk about new policies, while shattered Tories agonised and argued about what kind of leader they wanted next. But over the past four days, two huge and historic moments have finally begun to deliver signs of a “reset” of British politics.

Last Wednesday saw the first budget delivered by a female chancellor of the exchequer, Rachel Reeves.

Then on Saturday, 44-year-old Kemi Badenoch, born of Nigerian parents and brought up there, became the first Black politician to be elected as leader of one of the UK’s main political parties.

Both Reeves and Badenoch marked their moments in some style: Reeves with a spectacular high-risk, high-tax and borrowing budget, and Badenoch with a pledge to reimagine “what the Conservative party needs to be over the next five, 10 and 20 years”.

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One senior Tory at Saturday’s leadership event in central London said: “We have an intriguing battle in prospect now. Labour has laid out its store in no uncertain terms. Big tax, big spend. Now we under our new leader have to work out how to respond. What kind of party are we? We have to get this right but don’t need to be in any great rush.”

That said, Badenoch has to start making decisions almost immediately. Lab our cabinet ministers have been going around after the budget saying, “we have made our choices”, and “we have gone big” with £40bn of tax increases and changes to fiscal rules that allow massive extra borrowing. Now they are challenging the Tories to respond.

In the next fortnight there will be votes in the Commons on Reeves’s blockbuster £25.7bn move to increase employers national insurance contributions. The NI measure requires legislation of its own before it can be implemented. There will also be other votes on changing the fiscal rules to allow the huge sums of extra borrowing, and new inheritance tax arrangements for owners of farms, which the Tories hate.

All require decisions by Badenoch. Will she oppose Labour’s plans to spend on services and invest in infrastructure and if so what is the message that sends? Cabinet minister Pat McFadden, the chancellor of the Duchy of Lancaster, sees the dividing lines sharply now: “If the Tories want to go round the country opposing every new public investment in schools and hospitals they can be our guests.”

This all moves on from the pre and immediate post-election period when the two parties were both hedging bets. “The budget turns the page on that,” says another cabinet minister. No one in Labour is pretending that everything is set fair or easy now the budget is out of the way. There are worries about growth projections being so low despite all the extra spending.

Reeves stressed to the Observer that reform of services is now the key and that money will on its own not create a better public realm.

“Now we have fixed the foundations of our economy I am going for growth and I am going for reform,” she said. “Because we cannot tax and spend our way to prosperity nor can we tax and spend our way to better services. Instead, we need economic growth and we need economic reform.”

But Badenoch will not be allowed much of a honeymoon. This weekend she will begin choosing her shadow cabinet before she holds its first meeting on Tuesday. Already, former foreign secretary James Cleverly, Steve Barclay, former health secretary, and Jeremy Hunt, the former chancellor and foreign secretary, have said they do not want to serve.

Whether Jenrick agrees to do so remains to be seen. Then on Wednesday she will face Keir Starmer for the first time at prime minister’s questions.

Badenoch was congratulated by several of her predecessors, including Sunak, who posted on social media: “I know that she will be a superb leader of our great party” while former prime minister Boris Johnson praised her “courage and clarity” and said she “brings a much needed zing and zap to the Conservative party”.

The prime minister, Sir Keir Starmer, said: “The first Black leader of a Westminster party is a proud moment for our country.” He added: “I look forward to working with you and your party in the interests of the British people.”

The Lib Dem Leader Sir Ed Davey also congratulated Badenoch, saying “the first Black leader of a major UK political party is a historic moment for the country.”

But Davey and his party also see the election of Badenoch as a huge opportunity for the Lib Dems to hold on to the former Tory voters they gained in July. “This leadership contest has shown the Conservative party have abandoned the centre ground of British politics,” Davey said.