King Charles will say the UK and France must stand united in the face of a “multitude of complex threats”, when he speaks at a state banquet for French President Emmanuel Macron.

Macron and his wife Brigitte will be welcomed by the King and Queen Camilla and the Prince and Princess of Wales, as they arrive for a three-day state visit – the first by a French president since 2008, and the first by a European Union leader since Brexit.

Later, the issue of how to stop small boats crossing the Channel is expected to discussed at a UK-France summit that will be hosted by the prime minister.

Downing Street has said the UK’s relationship with France is “key” to tackling this among other issues.

“We expect to make good progress on a wide range of priorities, including migration, growth, defence and security, which will deliver on the interests of both the British and the French public,” a spokesman for No 10 said.

Sylvie Bermann, who was the French Ambassador to the UK from 2014 to 2017, described the small boats issue as difficult but said that France was “making progress” on it.

Responding to criticism within the UK that the British government has given too much money to France to try and deter small boat crossings without seeing any results so far, Ms Bermann said: “The UK is paying because we [France] is doing the job for the UK… you can’t prevent all of them [small boats] but we are doing our best.”

Sir Keir Starmer and Macron are also expected to speak by phone to other allied nations who are looking to support any future peace deal in Ukraine.

A state visit is a “soft power” opportunity to strengthen partnerships, with the French visit set to reinforce links with the UK at a time of uncertainty about the US stance on issues such as military backing for Ukraine.

The state banquet will be a highlight of the trip, with famous faces, a showcase menu and a message from the King about the “shared history and culture between our two peoples”.

The King’s speech will warn of threats in defence, technology and climate change.

“For centuries our citizens have admired each other, amused each other, and imitated each other,” the King will say at Tuesday evening’s banquet, which will be held at Windsor Castle, as Buckingham Palace is being renovated.

He will warn of current risks “emanating from multiple directions” and challenges that “know no borders” from which “no fortress can protect us”.

“Our two nations share not only values, but also the tireless determination to act on them in the world,” the state banquet speech will say.

The start of the visit on Tuesday will see ceremonial spectacles, with senior members of the Royal Family ready to greet the French visitors and to celebrate the “entente cordiale”, in the first French state visit since 2008.

Prince William and Catherine will greet the French president and his wife when their plane touches down at RAF Northolt.

King Charles and the Queen will then formally welcome them on a dais that has been built in Windsor town centre.

There will be horses, as well as political horse-trading, with a carriage procession through Windsor, ahead of a royal salute and military parade at Windsor Castle.

On Wednesday, Macron will see a horse that he gave to the late Queen Elizabeth II, to mark her Platinum Jubilee in 2022.

The French president and his wife are also set to visit the tomb of the late Queen, during their stay in Windsor.

The UK government has spoken of wanting to “re-set” post-Brexit relations with European neighbours and Macron’s visit will be a public endorsement of the longstanding alliance with France.

MPs and peers will be able to hear Macron when he gives a speech to the Houses of Parliament.

Advances in science will be highlighted during the visit, with examples of artificial intelligence and innovative technology being shown to the French visitors at Imperial College London.

King Charles and Queen Camilla carried out a state visit to France in 2023, where he received a standing ovation for his speech to the French Senate.

He had given a strongly worded message of support for Ukraine after Russia’s “horrifying” invasion. The King had also highlighted the “existential challenge” of climate change.