Brexit is a 'massive economic opportunity': PM Johnson

British Prime Minister Boris Johnson on Saturday said Brexit was a "massive economic opportunity" but had been treated under his predecessor Theresa May as "an impending adverse weather event".

In a speech in Manchester where he pledged new investment in Leave-voting areas, Johnson promised to step up negotiations on post-Brexit trade deals and set up free ports to boost the economy.

"When people voted to leave the European Union, they were not just voting against Brussels, they were voting against London too," he said.

Johnson promised to give more powers to local communities, as well as boost broadband and transport infrastructure in a speech focused on domestic issues.

"Taking back control doesn't just apply to Westminster regaining sovereignty from the EU, it means our cities and counties and towns becoming more self-governing," he said.

"Leaving the EU is a massive economic opportunity to do things we've not been allowed to do for decades," he said.

Asked about the prospect of Brexit negotiations, Johnson said he was willing to engage with EU partners but only if the backstop clause was removed from the current divorce agreement struck by May.

The backstop seeks to ensure a free-flowing post-Brexit border between British Northern Ireland and the Republic of Ireland, an EU member state, in all eventualities.

"The approach of the UK government is not going to be disengaged or aloof or waiting for them to come to us, we are going to try to solve this problem," he said.

"We can't do it as long as that anti-democratic backstop, that backstop that seeks to divide our country, divide the UK, remains in place. We need to get it out and then we can make progress."

The new leader earlier tried to dampen speculation he could call an early election.

The former mayor of London, who only took charge on Wednesday, has promised to take Britain out of the EU by the latest deadline of October 31 -- deal or no deal.

But he has focused on domestic priorities in his first few days in office, including a pledge on Friday to reverse drastic cuts to the police force made under May.

Commentators have speculated that he could be preparing to call a general election, hoping to regain the Conservative majority that May lost at the polls in 2017.

Johnson on Friday "absolutely" ruled out initiating such a poll before Britain leaves the bloc.

"The British people voted in 2015, in 2016, in 2017," he said during a visit to the central English city of Birmingham.

"What they want us to do is deliver on their mandate, come out of the EU on October 31.

"They don't want another electoral event, they don't want a referendum, they don't want a general election."

However, Britons could be headed to the polls if MPs bring down Johnson's new government in a no-confidence vote in order to try and prevent a no-deal Brexit from happening.

Britain voted 52 per cent in favour of leaving the European Union in a shock 2016 referendum that partially reflected deep resentment over economic inequality.

Johnson said Saturday's speech intended to "set out his vision to rebalance power, growth, and productivity across the UK".

May also came to power promising to fight Britain's "burning injustices" but her domestic agenda was overwhelmed by Brexit negotiations and her failed attempts to persuade parliament to vote in favour of her exit deal.