Twelve months before Gordon Brown lost power, Labour suffered deep losses at the 2009 local elections, slumping to just 23% of the vote and triggering an abortive putsch, spearheaded by the work and pensions secretary James Purnell.

In the event, Labour scraped a slightly less humiliating 29% at the general election the following May, but Brown’s anxious colleagues were correct to read the council polls as a harbinger of defeat.

Across England and Wales this weekend, Conservative politicians in vulnerable seats (which, given the national polls, means most of them) will be scrutinising local results for signs of their fate.

Election experts caution that there are good reasons not to read across directly from local elections to the national polls that follow.

Turnout in local elections tends to be much lower than at general elections, with party loyalists more likely to turn out, and many of the mayoral races feature local issues and strong personalities, so cannot be read as just a test of resilience.

Ben Houchen’s victory in the Tees Valley mayoral vote buoyed the Conservative mood, for example – but as Labour pointed out, it came with a swing of more than 16%, which would wipe out every local Tory MP – even if Simon Clarke (Middlesbrough South and East Cleveland) or Jacob Young (Redcar) had Houchen’s personal pulling power.

Specific characteristics of the current political map also make this week’s results harder to compare with the past.

Recent byelection wins for Labour in Mid-Bedfordshire (Conservative since 1931) and the Liberal Democrats in North Shropshire (a safe Conservative seat since the constituency’s creation in 1832, bar a Liberal MP 1904-06) suggest seismic shifts in electoral geography that make parliamentary results harder to predict.

There is also more fragmentation, with the Greens on the left and Reform on the right leeching votes away from the two main parties.

Neither of these factors offers any comfort to Rishi Sunak’s party, however: recent defeats in areas previously considered unwinnable for opposition parties point to shrewd tactical voting, apparently driven by a determined desire to vote the Tories out. The Lib Dems suggested on Friday they could see early evidence of this at work in local results too.

Meanwhile, poll watchers expect many Green voters to fall in behind Labour when presented with the opportunity of removing Sunak from power later this year, while Reform voters appear less likely to peel away to the Tories – again, scant comfort for Sunak’s MPs.

It has not been uncommon for the public to punish the governing party in local elections without being prepared to hand over the reins of power.

Ed Miliband achieved a higher share of the vote than David Cameron’s Tories at local polls from 2011 to 2014, with Labour’s performance peaking at 38% in 2012, as measured by Prof John Curtice’s “projected national share”. Yet when it came to the general election in 2015, Cameron’s party won a comfortable outright majority as the Lib Dem vote collapsed and Miliband was unable to convince the public to make him prime minister.

The Conservatives were keen to hint that a similar phenomenon could have been at play in this week’s polls, with the party chair, Richard Holden, suggesting they were “typical for a government in midterm”.

Even setting aside the fact that four years-plus into a parliament is definitively not “midterm”, the problem with this argument is that these latest results are pointing in exactly the same direction as every other indicator has been for many months.

Just as in the run-up to 2010 – and in the mid-1990s, when Tony Blair’s Labour began overhauling a tired Tory government at local polls – the clear message is that the public wants change.

Sunak and Holden hammered home their familiar policy messages on Friday – Rwanda, tax cuts, defence – but every recent test of public opinion, including this weekend’s results, suggests few are prepared to give them a hearing.

Like Brown’s peers, Sunak’s colleagues appeared unlikely to move against him, with even the Boris Johnson superfan Andrea Jenkyns throwing in the towel. But as in 2009, the incumbents would be right to read this final message from voters before the general election as foreshadowing the end of a political era.