At least 45,000 security personnel are set to be in place on the streets, rooftops and inside buildings

Paris is set for the biggest security operation in Olympic history when the Games return to the city for the first time in a century.

The “lone wolf” terrorist has been identified as the main danger to an opening ceremony which will see 160 boats take to the River Seine carrying almost 10,000 athletes and officials. At least 45,000 security personnel will be in place on the streets, rooftops and inside buildings.

A fleet of tourist vessels and restaurant boats will wend its way along the 6km (3.5m) route from the Austerlitz Bridge, close to Notre Dame, to the banks by the Eiffel Tower. French President Emmanuel Macron admitted the ceremony on Friday, July 26 could be moved inside a stadium if safety cannot be guaranteed. But organisers told the Mirror that the "show must go on".

They insisted "there is no Plan B" for a parade of athletes which will be seen by a worldwide TV audience of around 1bn. Another 350,000 spectators are expected to line the route, with 100,000 of them paying for front row seats. The rest will watch for free.

Paris 2024 chiefs told how this summer’s showcase has taken inspiration from the success of London 2012. The iconic monuments and buildings of the city of love are being used as a backdrop to venues, just as they were in London.

The British Olympic Association has spent the past week putting the finishing touches to the three training bases for our stars. There were a series of meetings involving key performance directors including cycling, athletics, gymnastics and swimming. And the French have drawn on the expertise and experience of the Brits in terms of organisation, and security. Mark England, Team GB’s Chef de Mission, said: “We are inside the IOC security plan and the organising committee security plans.

“We had the opportunity to interrogate that carefully, and we have every confidence in plans put in place. We go in with our eyes open and believe we will have a ceremony that will be nothing short of spectacular and will set the tone for the remainder of the Games.”

Just as in London 12 years ago, military personnel may be called up to bolster the ring of steel around the opening ceremony. They could prove a vital addition this summer, just as they were in London, with 392 events across 19 days.

“We will take the lessons from previous Games, borrow from the best,” said a Paris 2024 spokesperson.

“Again, there’s a kind of echo of 2012 in the sense that there are talks about using the army. The last time an event like this was organised here was 100 years ago. We make people aware of the scale of it. The FIFA World Cup sells 2.9m tickets over four weeks. This is just under 11m tickets in just over two weeks. There are more than 30 World Championships being organised simultaneously.

“If you talk to the head of security, what is the biggest challenge in the end? It is 10 events at 10 venues at the same time.”

Organisers say one in 20 of more than 7m tickets sold, around 500,000, have gone to UK addresses. The Brits are coming to Paris, second only to the French in terms of sales so far, above the US, Germany, Holland and Belgium. A third of the 400,000 which last went on sale in November were under 50 Euros (£42). Tickets for the opening ceremony are 90-2,700 Euros (£76 to £2,307). Some Team GB athletes may do a day trip to travel down the Seine, then go back home.

Others will head to St Germain-en-Laye, for athletics, our performance HQ in Clichy, with its own boxing ring, or Reims, and the 50m pool being used for our prep camp there. The IOC has a "very high level of confidence that the French authorities will make the Games safe". Just weeks ago, Paris civic chiefs gave detailed documentation, analysed by security experts, outlining the plans to ensure security throughout the event.

Held outdoors for the first time in Olympic history, the demands of an opening ceremony outside are highly complex. A lone wolf, reminiscent of the assassin hired in the 1963 Frederick Forsyth thriller "The Day of the Jackal", is a real fear.

But the IOC said: “All the necessary resources are being mobilised, with around 45,000 security personnel for the opening ceremony and around 35,000 for each of the other days, 24 hours a day.”

Private security will also have to be used after recruitment of police officers became a problem. The attack in December, in which a German teen was stabbed to death near the Eiffel Tower, has created new uncertainty. The chaotic 2022 Champions League final between Liverpool and Real Madrid in Paris also raised concerns. Thousands of unruly fans roamed the city, with police forced to use tear gas.

But there are also real grounds for optimism in Paris, which held the Games in 1900, and 1924. The Trocadero, opposite the Eiffel Tower, will host a daily ‘champions park’.

Around 13,000 fans will get the chance to see medalists after their events and watch the action on giant screens for free. British triathlon legend Alistair Brownlee will run with 2024 fun runners in a marathon. Open to the public, the event takes place on the day before the women’s marathon, which will be the last event of the Games.

Almost 2m tickets are being sold for the football tournament at stadia across France; the US Dream Team will play basketball at a 27,000-seater arena in Lille; cycling will see the Champs Elysees as a backdrop, just as in the Tour de France; for Brits in France this summer, thousands of provincial towns will be showing the action, and some outdoor events will be free to watch in Paris.

But in little more than 150 days, the curtain goes up on the Greatest Show on Earth, and the biggest security operation in France’s history.