Labour is facing recriminations after being trounced by the Tories in a critical by-election and losing control of a string of councils in England.
Keir Starmer said the party had "lost the trust of working people" as he came under fire over Labour's defeat in the Hartlepool by-election.
There was also grim news for Labour in contests for English councils and a landslide victory for the Tories in the Tees Valley mayoral battle.
But Wales offered hope to the party where First Minister Mark Drakeford was on course to form a Government after defying gloomy polls.
There was drama in Scotland where the SNP won three new seats as Nicola Sturgeon presses for a fresh mandate for another independence referendum.
Results will continue to flood in on Saturday and into Sunday, with Labour hoping to win several key mayoral contests, including London, Greater Manchester and the West Midlands.
The Welsh and Scottish Parliament results should become clear on Saturday - with all eyes on Edinburgh as Ms Sturgeon prepares for a clash with Boris Johnson over independence.
Here's what you need to know about the results so far.
Knives out for Keir Starmer after Hartlepool by-election defeat
Labour's hopes of rebuilding after the disastrous 2019 election were dealt a fresh blow after the Tories won a key by-election in Hartlepool.
Tory Jill Mortimer overturned Labour’s 3,595 majority and won the seat with a whopping 6,940 majority of her own - increasing the Tory vote by 23%.
The result represents a 16% swing from Labour to the Tories in a seat that has been red for decades.
Critics from the Labour left tore into Mr Starmer over the failure to retain Hartlepool, which prompted soul searching across the party.
The Labour leader acknowledged the scale of the challenge, saying Labour had "lost the trust of working people".
"I'm bitterly disappointed in the result and I take full responsibility for the results - and I will take full responsibility for fixing this," he said.
On Friday, he failed to deny swirling rumours that he would reshuffle his top team.
There was also bad news among English councils. With results available from 74 out of 143 councils, the Conservatives had a net gain of six authorities and 158 seats, and Labour a net loss of four authorities and 156 seats.
But Labour's Ros Jones was re-elected Doncaster mayor while Joanne Anderson became Liverpool's first black female mayor.
Tories win key mayoral race - as they eye West Midlands
Tory Ben Houchen was re-elected as Tees Valley mayor by a landslide, taking almost 73% of the vote at the first count.
His victory cements the Tory presence in the so-called Red Wall - seats in Labour's traditional heartlands in the north and Midlands.
It was regarded as one of the "big three" races of the bumper local elections, alongside Hartlepool and the West Midlands.
Results should come on Saturday for the West Midlands mayoral race, where Labour's Liam Byrne is attempting to topple ex-John Lewis boss Andy Street.
However the contest could be close, with the Tories gunning to retain the mayoralty.
Labour on course to form a Government in Wales
After a grim set of results in England, there was hope for Labour in Wales as the party looked set to win the Senedd election and lead the Welsh Government.
First Minister Mark Drakeford said his party had "exceeded expectations" as it ended Friday with 30 seats, just one short of a majority.
Gloomy polls had predicted Labour was at risk of its worst result and could win fewer than 22 seats.
But the party lost just one of Wales' red wall seats - Vale of Clwyd - to the Tories, and snatched Rhondda from Plaid Cymru founder Leanne Wood.
The results of the last few seats will be announced on Saturday but Labour is in a position to form a Government even if it falls short of the required 31 majority.
SNP hopes for independence majority on a knife edge
Nicola Sturgeon has vowed to press ahead with a fresh independence referendum as her party's hopes winning an outright majority in the Scottish Parliament hung in the balance.
The SNP needs 65 seats to win a majority at Holyrood, which Ms Sturgeon has said would give her a clear mandate to demand another border poll.
It won 39 of the 48 declared seats on Friday, snatching Ayr and Edinburgh Central from the Tories and East Lothian from Labour.
But Labour's Jackie Baillie held onto Dumbarton, Scotland's most marginal seat, which the SNP had been targeting.
Counting continues on Saturday, with the results expected to become clearer in the afternoon.
But a clash is coming whatever the result, as the Tories insisted that another referendum would be "irresponsible".
"We think this is a complete distraction," Environment Secretary George Eustice told Times Radio.
"It would be irresponsible to have another divisive referendum and another bout of constitutional debate at a time when we are charting our way out of this pandemic and when we've got to really focus on economic recovery.
"We think it's completely the wrong thing to be doing. We had a referendum just a little over five years ago and that settled the issue."
Encouraging results for Greens and Lib Dems
There were encouraging results for the Greens, with the party boosting their numbers of councillors in England to 84 - up 54 - with 91 out of 143 councils declared.
While the Greens don't control any councils, it elected its first councillors in Stockport, Northumberland, Hastings and Derbyshire.
"We are winning seats in areas that have traditionally been thought of as Labour and Conservative," co-leader Jonathan Bartley said.
The Lib Dems kept control of Mole Valley, in Surrey, and made gains in Cambridgeshire, pushing the council into no overall control.
In Stockport, the Lib Dems are now the largest party and could now form a minority administration.