It was during an emergency trip to the local B&Q last Thursday that a Lib Dem staffer was faced with the final and most bizarre decision of a long and gruelling byelection campaign: which mallet? Constituents were still casting their votes and the party was by no means confident of victory. Yet late on Wednesday evening, party chiefs had decided that should the Lib Dems pull off a genuine byelection shock in Chesham and Amersham, an image of leader Ed Davey bashing down a blue wall with an orange mallet was just too good an opportunity to pass up. By some miracle, 80 blue boxes had been ordered and delivered in time to make the wall. As for the mallet, there was a tricky choice. Of the two possible candidates, one was so enormous and hefty that it risked turning a photo op into a health and safety disaster. The other was a little on the small side, but was at least orange. The staffer opted for the smaller model. In the event, some viewers did suggest Davey could have done with a bigger prop as he duly bashed through the boxes before the cameras on Friday. Yet having defied expectations and provided further evidence of a profound political realignment in England, the sight of a tiny orange hammer having an unexpectedly big impact made for a fitting metaphor. The extraordinary result, a 25-point swing that turned a safe Tory seat into an 8,000-vote majority for the Lib Dems’ Sarah Green, has led to immediate and profound questions. Boris Johnson, previously seen as unbeatable, has suffered a shock defeat. While senior Tories have been insisting that local opposition to the HS2 line and planning reform proposals were cutely exploited by the Lib Dems, others see the result as confirmation that Johnson’s pursuit of former Labour voters in the so-called red wall has left his party’s own southern masonry exposed. To Davey, the result was a sign that Johnson, whose political superpower has been to say different things to different audiences, may have a limited shelf life. “He is essentially saying to lots of people in the south, ‘you are not my priority’. And people are hearing that. He is now going to have to fight on two fronts and he will be exposed when he tries to change his tune, trying to please everybody. You have to make some choices.” In the monsoon-like rain that fell on the constituency last Friday, it was still easy to find voters who confirmed that an expected trickle of support away from the Tories had turned into a torrent. Nobody who spoke to the Observer wanted to say they had supported the government, and several spoke of a personal dislike of Johnson’s leadership and his handling of the pandemic. For Matthew Bell, an electrician, it was a combination of Johnson personally and local gripes that persuaded him to switch. “I have voted Tory all my life,” he said. “I think the inaction over the Covid pandemic was the worst. They were so slow to react. She [Green] did a very good campaign. The Tories considered it a safe seat and it was always going to be theirs.” But he doesn’t see the blue wall crumbling: “It’s a bloodied nose rather than a knockout.” David Schrader, 90, who grew up in the East End of London, has voted Conservative for at least the past 25 years. “I didn’t vote because my wife is ill, but I would have voted for the Lib Dems,” he said. His main objection to Johnson is that he hired Dominic Cummings, the Vote Leave chief who has turned on Johnson since quitting as his adviser. “He should take much more care choosing ministers and advisers like Cummings. No unelected person should have that much power.” Megan Hitchcock, a postgraduate student, persuaded her mother to switch. “HS2 was the main reason – that and the pandemic,” she said. Mary Ziegler, an assistant matron at a local private school, said she doesn’t think much about politics, but voted Lib Dem in the last election after switching from Labour. “This lockdown has been difficult,” she said. “[Johnson] says one thing and then changes his mind.” So is a Johnson-inspired realignment gaining pace? Local government expert Tony Travers, who is director of the LSE London, a research centre at the London School of Economics, said the by-election result was more evidence of a gradual “erosion of the Tory party’s traditional rock-solid voter base in the south-east of England”. He pointed to strong indicators in the 2019 local elections, when the Conservatives faced sudden and huge losses of councillors in places such as Chelmsford, Chichester, East Cambridgeshire, Guildford, South Oxfordshire, Vale of White Horse, Winchester, Woking, Surrey Heath and Spelthorne. “Seven months later, the Tories won the general election,” he added, “but with the south-east recording the smallest Labour-to-Conservative swing of any region in England [3.4%], including London. Most recently, in this May’s county elections, the Conservatives, while gaining seats across England as whole, lost vote share in southern counties such as Kent, Surrey, East Sussex and Hertfordshire.” Travers said demographic changes help explain what has been going on: “In a typical year, more than 200,000 people move out of London to the south-east and east. Labour votes are, effectively, being exported to the wider region.” Robert Ford, professor of political science at Manchester university, agreed that while local factors helped, the result was in line with broader trends. “The defeat in Buckinghamshire,” he writes in the Observer, , “will send shivers down the spines of dozens of Conservatives representing southern Remain-leaning seats, where the Lib Dems surged in 2019. They include senior figures such as Dominic Raab, Jeremy Hunt and Michael Gove. “The EU referendum has accelerated political changes long in train, as demographics reshape the electorate and change the dividing lines of political competition. The Conservatives are on the wrong side of these changes. They are strongest among socially conservative white school leavers – a declining group in an electorate which is becoming more graduate-heavy and more ethnically diverse. They dominate among the old while struggling among the young.” Alarm bells are officially ringing for many senior Tories, but the immediate concern is over specific policies. “This was one byelection,” said former cabinet minister Damian Green, Tory MP for Ashford, Kent, when asked whether the Tories now had a serious problem. “But nonetheless we need to relearn the old lesson that you never take voters for granted.” He and many other Conservative MPs have been raising their concerns about changes to planning rules that would allow for the building of 300,000 more houses, and in so doing weaken the powers of local people to object to applications on their doorsteps. Another Tory MP, Sir Bob Neill, a former local government minister, said: “The government needs to recognise that while there is an acceptance that we need to build more homes, the planning system touches on the fundamental rights of individuals and communities who are affected by planning applications.” Former cabinet ministers MPs including Iain Duncan Smith and Theresa Villiers are also pressing for changes to the proposals. Former Tory MP and attorney general Dominic Grieve, whose former Beaconsfield seat borders Chesham and Amersham, said many Tories were deeply unhappy with what Johnson was offering: “These are places where Conservatives have deep reservations about Johnson and Johnsonism. They say that ‘yes we voted for him in 2019 because the alternative was that awful man Corbyn’ but they now don’t like what they see. They don’t like the cut of his jib.” So where next can the Lib Dems test their theory that the blue bricks are crumbling? Party figures are already getting excited by the prospect of former prime minister Theresa May being handed a top Nato job, as has been rumoured. Her Maidenhead seat is as true blue as they come – she secured a 19,000 majority in 2019 with 58% of the vote. Even closing that gap significantly, however, would help the Lib Dems prove their point. Another obvious target is Esher and Walton, the constituency of Dominic Raab. The foreign secretary fended off a strong challenge from Lib Dem Monica Harding at the last election, securing a slim majority of 2,743. Judging by the reactions of people at the constituency’s Hersham Green shopping centre, Raab will face another testing campaign whenever the next election is called. While Raab did have more tangible support than the Tories had in Amersham, he should be worried about people like 81-year-old Brian Williams, former managing director of a large shipping company who has only ever voted Tory. “It’s completely loused up,” he said. “I think this guy is the worst prime minister we’ve had in my lifetime. The sheer incompetence and stupidity. The lies and the falsehoods.” Should opponents of Johnson suddenly hope he is beatable? There are obvious notes of caution. Some analysts warn that while a Lib Dem victory in other liberal Tory seats is possible, a far broader Labour recovery in other areas would be needed to oust a Johnson government. Morale among many Labour MPs is perilously low. In less than two weeks, Labour is defending the West Yorkshire seat of Batley and Spen. Recent polling puts the Tories in the lead. Labour was not a serious contender in last week’s byelection, but even so it secured just 622 votes – fewer than the Greens. In Amersham last Friday, the name absent from most voters’ lips was Keir Starmer. Liz Riley, a postal worker, said: “Labour just can’t seem to find an inspiring leader any more.” However, in a sign of greater cooperation between the parties, Davey gave a broad hint that Lib Dem voters should back Labour in the Batley contest. “Political parties campaign where they can win,” he told the Observer. “We thought we could win in Chesham and Amersham. Labour didn’t campaign very much. In Batley and Spen, we will have a presence – we’ve got councillors there. But we’re not going to be able to, frankly, pour in the resources that we put into Chesham and Amersham. “Voters are far smarter than people give them credit for. Liberal Democrat voters may well notice that this is a Labour-held seat with the Tories in a close second, and they’ll draw their own conclusions. But that shouldn’t be stitched up in a back room by party leaders.” It amused Lib Dem staffers that the boxes that made up their blue wall prop had been delivered by courier from Grantham, birthplace of another true-blue export, Margaret Thatcher. While they will need some luck to take another byelection brick from the Tories, they now know that, however seemingly small the mallet, they have the tools to deliver damage.