Theresa May faced her first nationwide electoral test as Britain's prime minister on Thursday, as she toughened her Brexit position just weeks before a crucial general election.
Britons began choosing thousands of new local councillors in a vote that will be closely watched for proof of the strength of May's Conservatives, which opinion polls suggest are on course for a thumping victory in the June 8 parliamentary elections.
Nearly 5,000 local authority seats are being contested across England, Scotland and Wales, along with eight metropolitan mayoralties.
Experts caution however against using the results to predict the outcome of next month's vote, noting that such elections are normally fought on local issues and are often used to punish the sitting government.
But the proximity of the general election and the political upheaval caused by last year's shock Brexit referendum have created a unique context.
- 'Threats against Britain' -
May gave the European Union formal notice of Britain's intention to leave the bloc on March 29, and two weeks ago called a surprise general election.
She says she wants to strengthen her mandate as she heads into the Brexit negotiations, and is well aware the issue will be on many voters' minds on Thursday.
Speaking outside her Downing Street office on Wednesday, May took aim at Brussels for making "threats against Britain" over the divorce proceedings.
The two sides have clashed over the costs of the exit, prompting May to accuse the EU of toughening its stance in statements "deliberately timed to affect the result of the general election" next month.
European Parliament President Antonio Tajani on Thursday dismissed the claim, insisting that "no one is trying to influence the outcome".
The chief spokesman for European Commission head Jean-Claude Juncker had earlier chalked up May's comments to election campaign rhetoric.
"We are not naive. We know there is an election taking place in the United Kingdom," Margaritis Schinas said.
British opposition leaders have claimed that May is using the EU talks as a distraction from other issues, with Labour leader Jeremy Corbyn accusing her of "playing party games with Brexit".
- Local elections spillover -
Labour is more than 20 points behind the Conservatives in opinion polls, but the party says the local elections could show this to be inaccurate.
"Let's see what happens. That might be an interesting measure of how things are going more generally, and how accurate the polling is," a senior Labour source said.
Roger Scully, a politics professor at the University of Cardiff, said the national picture would inevitably have some effect on the vote.
"The Conservatives are doing very well and that is almost certainly likely to have some spillover into the local elections," he said.
"They will provide some vital information about the pattern of support and where parties are performing particularly strongly or weakly," added Anthony Wells of polling company YouGov.
But drawing a national picture will be made harder by the absence of council elections in England's biggest cities, where Labour is traditionally strong.
Polling stations opened at 7:00am (0600 GMT) and close at 10pm, with results due on Friday.
The smaller, pro-EU Liberal Democrats, who were almost wiped out in the 2015 general election after entering a coalition government with the Conservatives, are hoping to pick up some momentum for the June vote with gains on Thursday.
By contrast the anti-EU, anti-mass immigration UK Independence Party is predicted to lose most of its council seats as it struggles to define itself now that its principal goal -- Brexit -- is on its way to being achieved.
Meanwhile in Scotland, the local elections will indicate the strength of the ruling Scottish National Party, which has used the Brexit vote to call for a new referendum on independence.