When Theresa May flew in by helicopter to launch her general election campaign in the Bolton North East constituency that has returned a Labour MP for 20 years, she was accused of drafting in activists and distancing herself from the public during a brief appearance.

There was nothing scripted, however, about the reaction of 87-year-old Joan Bedson when the local Tory candidate knocked on her door. “I nearly needed mouth-to-mouth resuscitation,” said the retired librarian. “Labour campaign out here all the time, but I’ve never seen a Conservative candidate in all the years I have lived here. I was just saying that to friends yesterday. And now I’ve been visited by the candidate.”

The appearance of Conservative hopeful James Daly on her doorstep may have been a shock, but the party’s heightened activity in the constituency is not random. The Tory successes in last week’s local elections included gaining majority control of Lancashire county council, displacing Labour as the biggest party. Yet even before the red rose of Lancashire had turned blue, Conservative strategists had their sights trained on a revival in some of the region’s Westminster seats.

The local election results have raised their hopes that a combination of the Brexit vote, May’s personal popularity and the defection of Ukip voters gives them a chance of succeeding where years of talk about creating a “northern powerhouse” failed.

Northern seats in play range from traditional marginals to constituencies like Bolton North East, which have been beyond the Tory grasp since the New Labour landslide 20 years ago. They hope the voters who previously voted for Ukip will help to secure them.

Tory sights are set on the likes of Chester, Halifax, Lancaster and Fleetwood, Bury South, Chorley and Batley and Spen. The shock Tory victory in the Tees Valley mayoral race has raised hopes in the party of winning in places like Hartlepool, which has returned a Labour MP since the 1960s.

One Tory MP was amazed recently to be dispatched to Scunthorpe. “Scunthorpe! It’s a Labour steel town where there is a surge towards the Conservatives. It is working-class people who don’t trust [Jeremy] Corbyn and do trust us, but they also want us to deliver.”

The last time the Conservatives won the constituency containing Scunthorpe was in 1983, when the party scraped home in its landslide victory. The shifting electoral map is causing its own problems. “The issue is going to be figuring out which are the real target seats,” said one senior Tory figure.

Back in Bolton, it is not all plain sailing for Daly’s bid for Westminster. The townspeople voted for Andy Burnham in the Manchester mayoral race. Out canvassing last week, there were still voters who closed the door after hearing the word “Conservative” and others who told activists that they were solidly Labour.

And for a Conservative campaign that has been attacked as too scripted, the attempt to win Bolton North East has already undergone a serious rewrite. Daly was drafted in as the candidate only last week after the initial choice, Abi Kay, pulled out for “personal reasons”.

There is also a sense that the Conservatives are aware that their brand is still toxic for many. Voters will initially struggle to find the word “Conservative” on the leaflets being posted through their letter-boxes. One side, headlined “strong and stable leadership in the national interest”, takes the form of a signed letter by May and has no mention of the party she leads. On the reverse, each mention of the party comes in a construction that makes it sound like a 1960s pop group, “Theresa May and the Conservatives”.

Joan Bedson was shocked when she opened her door to a Conservative candidate canvassing in Bolton North East. Photograph: Jon Super/The Observer

Yet there are tangible signs that the political plates of Bolton are beginning to loosen. Both a liking for May and concern over Corbyn are raised by voters on the doorstep.

One explains that she voted for Burnham in the mayoral race – “he’s a good local man and I backed him” – but is undecided on next month’s general election. “I’m not sure about Jeremy Corbyn at all – he hasn’t got the oomph to be leader,” she says. “But then I’m not sure about Theresa May, either. She voted to stay in the EU, and I voted to leave. It’s difficult – I’m undecided for the election.”

Another voter raises similar concerns. “I’ve always voted Labour, but they haven’t got a very good leader. He’s a bit iffy. But the thing is, the Labour MP here is quite good. It would be quite unfair to lose because of who the leader is. But Theresa May’s a very strong leader, isn’t she?”

Matthew Wright, 56, out for a walk with Dolly his border collie, will still vote Labour despite his frustrations over the party’s campaigning so far. He has sympathy with Corbyn. “I think Jeremy Corbyn is a really genuine man,” he says. “Probably too genuine. He talks about the sort of policies that I have always wanted to vote for, but it’s no good if you’re never going to be in power. I will vote for Labour, but under sufferance. The Tories must be rubbing their hands with glee.”

As with other Labour candidates in close races, Sir David Crausby, who has contested the seat since 1992 and held it since 1997, is attempting to focus the election on his performance as MP.

“I have sort of protected my majority since 2005 of around 4,000,” he says. “That has been against the national trend, really. It is not a safe Labour seat. It is a seat with four Labour wards in the south and three Tory wards in the north.

“I’m an independent-minded local MP. If I don’t agree with the leadership of the party, I don’t vote for it. I don’t rebel all the time, but things like the Iraq war, tuition fees – I rebelled.

“In the Asian community, Corbyn is not a factor at all. Among the white working classes as we see it, he is. I am getting squeezed a little bit, so we are concerned about that.

“My argument is, he isn’t on the ballot paper here – it is me. We are not a presidency. We vote for individual MPs. If I don’t agree with what Jeremy Corbyn says, then I won’t vote for it. It will be me on the leaflets.”

Matthew Wright with his dog Dolly in Bolton. Jeremy Corbyn talked about policies he wanted to vote for, but that was no good if he was never going to be in power. Photograph: Jon Super/The Observer

Despite the apparent appeal of May, resistance to the Conservatives among a certain group of northern voters means some find themselves with a dilemma. It is the obvious anguish of Stephen Thomasson, 65, a retired fireman, that suggests some may now be thinking the previously unthinkable.

“I have voted Labour all my life, all my life, but this time I am voting for the Conservatives,” he says, sitting in the shadow of Bolton’s grand town hall. “It breaks my heart to vote Tory, but that is what I am going to do. It breaks my heart. I have a lot of friends in the same place, all voted Labour all their lives, but are now voting Tory.

“I just do not trust Jeremy Corbyn. I think things are dangerous, with what we’ve seeing around the word and in North Korea, and I’m worried the first thing he’d do is get rid of nuclear weapons. I don’t know what he’d do for working people in this country, for pensions.

“Theresa May is doing well, not just on Brexit but on everything so far. Corbyn will let Europe walk all over us.”