France is bracing for fresh “violent” protests - and not just against pension reform - amid hang-wringing over Emmanuel Macron’s “humiliation” for postponing King Charles III’s state visit.

Demonstrations against the French president’s pension reform to raise the retirement age from 62 to 64 were expected in various cities around the country, including Brest, Montpellier, Nice and Dijon.

But police were reportedly most concerned about a separate demonstration at Saint Solines, central France, where thousands of people were expected to turn out to a "high-risk" protest against the deployment of new water-storage infrastructure for agricultural irrigation, despite an official ban on the gathering.

More than 3,000 police officers will face off against what they predicted could be up to 1,500 "violent activists" from among a crowd of up to 10,000 today. The construction site was the scene of very violent clashes last October when work was suspended.

The Sainte-Soline water reserve is the second of 16 such installations, part of a project developed by a group of 400 farmers organised in a water cooperative to significantly reduce mains water usage in summer. Opponents claim the "megabasins" are wrongly reserved for large export-oriented grain farms and deprive the community of access to the essential resource.

The protests come a day after Mr Macron postponed King Charles III’s first state visit to France due to fears of violence.

Le Figaro's front page read: "Charles III: at the heart of the crisis, an avowal of powerlessness". Its editorial called the postponement a "humiliation", saying France's "Republican monarch" caved in to a bunch of "half-woke half-Bolivarian revolutionaries”.

But an Elysée source was quoted as saying: "A state visit between our two countries cannot be mezzo voce, especially after the Boris Johnson period. It must be pleasant and festive for the King of England and Head of the Commonwealth."

Laurent Berger, head of the CFDT union, France’s largest, on Friday urged Mr Macron to put the pension reform "on hold for six months" to allow tensions to cool down. But the president said that while he was "at unions' disposal" to discuss issues relating to labour, the pension reform was now in the hands of the Constitutional Council, France's highest constitutional court, which must rule within a month whether it is viable.

With public opinion firmly behind the protesters, unions have called another day of mass strike action next Tuesday. Meanwhile, a public opinion battle appears to have erupted over who is guilty in demo clashes - protesters or police.

Mr Macron condemned the latest burst of violence overnight Thursday, which saw 441 police officers injured and 900 fires lit, while a human rights watchdog criticised the "excessive use of force" by police during recent demonstrations.

Fearful of inflaming tensions, Paris' police chief on Friday night launched an investigation after Le Monde and France Info on Friday released extracts of a recording in which motorised anti-riot police can be heard insulting and slapping youths they had just arrested after last Monday's protests.

"Wipe that smile off your face," one can be heard saying before slapping him. "Will you shut your mouth or do you want another one?," he can be heard before slapping him again.

"I can tell you we broke some, elbows and mouths,” he can be heard adding.

France was expected to experience limited cancellations and delays in planes and trains, with 33 per cent of flights from Paris’ Orly airport cancelled on Sunday and 20 per cent to and from Roissy Charles de Gaulle. On Monday, the figure was put at 20 per cent in both.

However, in a glimmer of hope for Parisians, a rubbish collectors' strike that has seen 10,000 tons of bin bags pile up in the streets of the capital may have reached a turning point after unionists ended their blockage of two of the capital's three incinerators and the third was requisitioned.

The garbage is currently fouling up Paris, causing a major health hazard. Piles of bin bags have also been convenient bonfires for pension reform protesters.