On a cold, crisp day in a prosperous neighbourhood in Earley, Berkshire, Phillip Lee, the former Tory minister now running for the Lib Dems, has reason to be cheerful. In the space of a few minutes, he has traipsed up the long gravel drives to speak to a couple of voters pledging to switch from the Conservatives to back him.

And yet it is clear that Lee, whose concerns about Brexit drove him to give up a safe Tory seat to fight the Remain cause, is aware that there are frustrating obstacles that could prove critical in his quest to overturn the 18,000 majority of the arch-Brexiter John Redwood. The failure of a bigger pro-Remain pact looms large. “Alastair Campbell was out supporting me yesterday,” he says. “He’s pretty depressed about it.”

Lee also admits to some difficulties created by his party’s own policy – its commitment to revoke Brexit unilaterally should it win a majority. “It’s not helped,” he says. “I always say to people, ‘Look, we’ll revoke if we return 326 MPs to Westminster. If we get 326 Lib Dem MPs, that would be a historic moment’. I think you’ll have noticed it’s been dialled back quite heavily.

“My own view is we should’ve just said we are Remain. We’re for a second referendum, and we’re Remain. That was my own, personal view. I understand where [revoke] came from – the Liberal Democrat party is very democratic, and it’s what members wanted. But it has involved me having to talk a bit longer to soft Tories, basically.”

With less than a fortnight to go until what has been billed as the most important election in a generation, this was the week that two of the main protagonists – Labour and the Lib Dems – appeared to change tack.

Labour insiders said that the key battle was not now fighting off the Lib Dems in pro-Remain seats but retaining traditional Labour seats in the Midlands and north tempted to vote Tory. For the Lib Dems, talk of Jo Swinson becoming PM and revoking Brexit has been replaced by a more defensive plea for Remain voters to prevent a Tory majority by voting tactically for the party in key seats.

It was not long ago that the Lib Dems were imbued with confidence that Lee’s seat, Wokingham, was among well over 100 constituencies that it could realistically target thanks to its pro-Remain stance. But last week, a huge YouGov poll predicted it would win just 13 seats – representing a net gain of one compared with the last election.

In such circumstances, it is hardly surprising that the party has shifted its pitch to voters. When the Observer visited Wokingham last week, concern from Remainers about respecting the referendum result was a running theme. Many in this previously safe Tory seat spoke of their opposition to Jeremy Corbyn. There was also support for Lee, however, suggesting that it remains a tantalising battle. “We know from our canvass returns that it’s close,” says Lee. “We know this is a massive challenge, but every time I’ve been out, there have been switchers. Sometimes not so many, other times overwhelming. There has to be something happening.”

As for Labour, briefings last week suggested the Lib Dem threat had been overstated, meaning the party would throw its resources behind defending seats in the Midlands and the north that are critical to Boris Johnson’s hopes of a majority.

Caroline Flint and her party leader Jeremy Corbyn in Conisborough, near Doncaster, after last month’s flooding. Photograph: Lindsey Parnaby/AFP via Getty Images

Speaking to voters in Don Valley, one of the Labour seats the Tories are predicted to win, it is not hard to detect the danger. Standing on what was once the coal-stocking yard for the Yorkshire Main colliery, now a car park for the discount store Home Bargains, Desmond Hodgetts had no hesitation about who he will be voting for.

“Boris. He’s the only one who’s got the balls to sort this out with the EU,” he said. Caroline Flint, the Labour MP for Don Valley for the past 22 years, does “a brilliant job, but who does she work for? I don’t trust Corbyn and his little gang. If Labour had different leaders, I’d be voting for them,” said Hodgetts, a self-employed 57-year-old.

The views of a dozen or so voters in Edlington, five miles south of Doncaster, epitomise the challenges facing Labour in next week’s election. Several said they admired Flint, who has been vocal in backing her constituents’ pro-Brexit views in parliament, and who voted in favour of Johnson’s withdrawal deal before the election was called. But only a handful said they had made up their minds to back her. More were undecided, and some were doubtful whether they would vote at all.

The campaign was “tough”, said Flint, who is defending a majority of 5,169. “Clearly Brexit is dominating. I’d say on every other door in our mining villages, it’s Brexit that comes up. Even Remain voters say we should get on with it.”

In former pit villages such as Edlington, voters “don’t like the Tories, they don’t warm at all to Boris Johnson, but they want Brexit sorted. And the one thing that’s very clear is that they can look me in the eye and know I’ll vote for a deal as soon as possible if re-elected”, said Flint.

Neil Thomas said he would vote Conservative in order to get out of the EU. “I don’t like Boris, don’t get me wrong. This election is a tough one for lots of people. My dad was always Labour, but he’s for the Tories now because of all this Brexit. This area used to be rock-solid Labour, but it’s all split now.”

Flint said she was not aware of any change of tack from Labour HQ to step up the party’s appeal to pro-Brexit voters following the YouGov poll. But, she added, there was a real risk of people who felt their views had been sidelined not voting at all.

“We’ve got a fortnight to go,” she said on Friday morning. “I’m not taking anything for granted. We’re campaigning hard. But if I lose, we’ll lose 50 Labour seats in the north and Midlands, which would be terrible.”

However, senior figures inside Labour believe that talk of changing strategy is not really about the election but the first act in the battle for the post-election narrative about why Labour failed to win. Several Labour figures said they believed it was a move designed to blame pro-Remain figures in the party for defeat, and deflect from the personal unpopularity of Corbyn or the party’s radical policy platform.

“They are not changing tack,” said one insider. “This is about blaming everyone but themselves for the loss. The fact that we can’t make a decision on Brexit means the voters can’t trust us on anything else.”