Marine Le Pen's performance in France's presidential race cheered Brexit supporters, but many fear the likely winner Emmanuel Macron will play hardball in Britain's negotiations on leaving the European Union.
EU leaders are relieved at the prospect of a victory for Macron, a pro-European centrist, in a run-off on May 7 against eurosceptic far-right leader Le Pen.
But for commentators on all sides of the political divide in Britain, Macron spells bad news for Prime Minister Theresa May as she embarks on Brexit talks after her own expected re-election in June.
"Emmanuel Macron would be bad for Brexit and Theresa May," said the eurosceptic Daily Telegraph newspaper, which is close to May's Conservatives.
"French presidential favourite Macron may drive hard bargain in Brexit talks," said the left-leaning Guardian.
May formally notified the EU on March 29 of Britain's intention to end its 44-year-old membership, following the shock referendum vote for Brexit last June.
In order to curb mass migration into Britain, she intends to pull Britain out of Europe's single market, while still pressing for access for British firms.
But several EU leaders have warned Britain cannot "have its cake and eat it".
Macron dedicated a chapter to Europe and its benefits in his election manifesto, and on Brexit, said he would defend the integrity of the single market.
"All companies who have access to it must be subject to the same rules," he said.
In a rare honour for a presidential candidate, Macron met May in London in February, where he promised "a fair execution of Brexit protecting French and European interests".
But he told a rally of expatriate voters afterwards: "The best trade deal for Britain... is membership of the EU."
- 'Macron as the enemy' -
The Financial Times daily laid out several reasons why Macron as president "could make matters a good deal tougher for the British in Brexit talks".
"He is a convinced European" who will likely offer few concessions -- particularly on access to the single market for Britain's dominant financial services sector.
"Some analysts believe that as a former Rothschild banker, he will want to do everything possible to maximise Paris's position as a financial centre after Britain?s departure," the FT said.
Others take a more emotive view.
"I see Macron as the enemy," said Nigel Farage, the former leader of the UK Independence Party (UKIP) who was a key player in the Brexit vote, and now backs Le Pen.
"He wants Brussels to be even stronger, and I can't see that it's in our interests when the Junckers and others are all lining up to try and punish Britain," Farage told LBC radio, referring to European Commission president Jean-Claude Juncker.
Simon Tilford, deputy director of the Centre for European Reform, acknowledges that "on the face of it, it looks bad".
"Macron has taken quite a tough line on the whole issue of Brexit, arguing that the EU needs to take a tough line with Britain in order to set an example to other countries that might be tempted to follow a similar route," he told AFP.
"Whereas Marine Le Pen has expressed understanding for the British position."
However, he said "a tough line is not necessarily bad for Britain if it forces Britain to compromise and to be more honest about the trade-offs it faces".
He added: "From a European perspective, Britain has absolutely no incentive, or no interest, in the kind of political instability, or even chaos, that could follow the election of Marine Le Pen."