Theresa May is “waging a war against the poor” and risks leaving the country more divided than at any time in 50 years, former PM Gordon Brown has said.

Addressing Labour activists in Fife, he said poverty levels were set to eclipse those last seen in the early 1990s.

He acknowledged the challenge facing Labour but said “no Tory prime minister should ever be given a free hand”.

Mrs May has urged lifelong Labour voters who feel “deserted” by Jeremy Corbyn to put their trust in her.

In his biggest intervention to date in the election campaign, Mr Brown attacked the record of the Conservatives and the SNP in power and said a Labour government was needed more than ever.

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Earlier on Saturday, Labour’s deputy leader Tom Watson warned of a “Margaret Thatcher-style landslide” for the Conservatives if his party fails to turn around current poll numbers.

Labour had a “mountain to climb” to catch up with the Tories before 8 June’s vote, he conceded in an interview with the Guardian.

Mr Corbyn said both he and Mr Watson were “working flat out to get Labour elected” on 8 June.

Asked whether senior party figures were already admitting defeat, he replied: “Not at all.”

He added: “I am out round the whole country, the party is out round the country putting out the message we are for the many, not the few.”

‘Carte blanche’

Mr Brown – campaigning in his former constituency, which Labour lost to the SNP in 2015 – defended the legacy of the Labour governments of which he was a key figure and suggested they were under threat from the government’s squeeze on welfare spending allied to the rising cost of living.

Citing figures from the Institute for Fiscal Studies and the Joseph Rowntree Trust, he claimed the number of people deemed to be living in poverty had risen last year to levels last seen in the early 1990s and that the numbers were set to rise sharply by 2022.

“Mrs May says she wants to unite the country but she will create a country that is more divided economically and more socially polarised than at any time in the last 50 years,” he said.

“We have got to get MPs to Parliament to fight a war against poverty and stop this war against the poor.”

The prime minister, he suggested, wanted to turn the election into a “one-issue” campaign on Brexit and marginalise important subjects such as the future of the NHS, education and levels of inequality.

“She wants you to strengthen her hand with Europe but won’t tell you what that hand is. What she wants is a free hand.

“She wants carte blanche to do whatever you want. No prime minister should ever be given a blank cheque. No Conservative prime minister should ever be given a free hand.”

‘Checks and balances’

In his interview, Mr Watson asked for voters to consider that “a lot of local MPs are running on a good track record” when people head to the polling stations next month.

Speaking on a tour of marginal seats in Wales, Mr Watson said Labour had “terrifically exciting” proposals in its manifesto – a draft of which was leaked earlier this week – but he was concerned about how far behind Labour were.

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“If we get to 8 June and [Theresa May] still commands the lead in the polls that she had at the start of the election, she will command a Margaret Thatcher-style majority,” said Mr Watson, referring to the Tories’ 144- and 101-seat victories in 1983 and 1987 respectively.

Appealing for voters’ backing, he added: “A Conservative government with a 100 majority… it will be very hard for them to be held to account in the House of Commons. “It means there won’t be the usual checks and balances of democracy. All those things go out of the window.”

On Friday, Mrs May travelled to Tyne and Wear to appeal to an area that traditionally voted Labour.

“Proud and patriotic working-class people in towns and cities across Britain have not deserted the Labour Party – Jeremy Corbyn has deserted them,” she said.

“We respect that parents and grandparents taught their children and grandchildren that Labour was a party that shared their values and stood up for their community.

“But across the country today, traditional Labour supporters are increasingly looking at what Jeremy Corbyn believes in and are appalled.”