Jeremy Corbyn has said his party is in “permanent campaign mode” as he heads to Cornwall on a national tour that aims to place Labour on a more offensive footing.

The Labour leader has chosen dozens of Conservative-held seats across England and Wales, and SNP ones in Scotland, for a series of campaigning events to prepare for the next election.

The move comes after sources said there were tensions within Labour over whether the party was too defensive during the 2017 general election campaign after polls suggested major losses.

Corbyn said he wanted to take a “message of hope to marginal seats” as he explained that the focus on Tory-held seats, rather than those with Labour MPs, was about winning a parliamentary majority.

On Thursday he will start at a hospital in Truro and Falmouth where the Tory majority was cut from 6,526 to 2,457 in the June election, followed by a rally in Camborne and Redruth where it was reduced from over 7,004 to 1,577.

“This week I’m visiting the south-west. It’s a part of the country not thought of as traditionally Labour, but a Labour government would transform the lives of people across the south-west,” he said.

“The region suffers from widespread low pay and job insecurity. So Labour’s Real Living Wage of at least £10 an hour would be a real boost for many workers in the south-west.”

Corbyn’s whirlwind tour will be matched by visits for shadow cabinet members to a total of 100 marginal constituencies across England, Scotland and Wales.

The Tory Europhobes who destroyed the premiership of David Cameron are waiting to do exactly the same thing to Theresa May Diane Abbott, Shadow health secretary

Shadow home secretary Diane Abbott told the Guardian that the party was “ready to rumble” as she claimed the Tories had “never been more vulnerable”.

“The same group of fanatical Tory Europhobes who made John Major’s leadership miserable and destroyed the premiership of David Cameron are waiting to do exactly the same thing to Theresa May,” she said. “And we will be waiting when the Tories implode.”

Corbyn started campaigning immediately after the election with a rally in the Hastings and Rye constituency, where the home secretary, Amber Rudd, clung on with a wafer-thin majority of 346.

He has also travelled to Chingford and Woodford Green, represented by former Conservative leader Iain Duncan Smith, where there was a 15.2% swing towards Labour, cutting the majority from 8,386 to 2,438.

This leg of the tour, after a holiday with his wife, Laura Alvarez in Croatia, will include dozens of small events and three major rallies in Redruth, on a beach in Southport and in Glasgow.”

Thursday’s events are focused on health after the Labour party chose to focus each week of the recess on a different issue.

Corbyn will be joined by shadow health secretary, Jonathan Ashworth, who told the Guardian that he wanted to persuade voters that Theresa May had failed on the NHS and that was “symbolic of her wider failures”.

Corbyn will travel from the south-west to Swindon South and Filton and Bradley Stoke. Later visits will take place in Milton Keynes, Carlisle, Copeland, Morecambe and Lunsdale, Rossendale and Darwen, Pendle, Blackpool North and Cleveleys and Bolton before heading to a number of SNP seats north of the border.

Almost all the seats, apart from two in Scotland, are those held by other parties where the majority was significantly cut in 2017 - defying expectations.