The event, which also celebrated a £2m redevelopment of the harbour, saw Sir Ben arrive on board a traditional scow with the Hon Mary Montagu Scott, commodore of the Beaulieu River Sailing Club and director of Beaulieu Enterprises. The pair led a fleet from Beaulieu River Sailing Club, which was formed 90 years ago under the patronage of Mary’s grandmother Pearl.

More than 800 berth and mooring holders welcomed them and watched the ceremony, where Sir Ben was presented with the freedom certificate by Lord Montagu. They were joined by Sir Chay Blythe, who was himself granted the ‘freedom of the river’ by Lord Montagu’s father at the original marina opening in 1971.

The celebrations continued with a regatta and games. Children took part on a crabbing competition and families competed in rowing and swimming challenges. There was a best dressed boat competition, judged by Sir Ben, and won by Kim Flury.

Lord Montagu said: “We were thrilled and indeed honoured to welcome Sir Ben Ainslie as our special guest to commemorate the completion of our rebuilt yacht harbour. With the recent Tokyo Games fresh in our minds, it is good to reflect that Sir Ben is the most successful sailor in Olympic history, winning medals at five consecutive Olympics from 1996. As a resident of the Isle of Wight, who will be sailing in the Solent, it occurred to me that safe harbouring in the Beaulieu River might occasionally be useful between races.”

Sir Ben Ainslie responded: “Sailing here with Mary just reminded me of what a wonderful sport sailing is and how lucky we are to be able to get out on the water in such beautiful surroundings as the Beaulieu River. I am not quite sure how we’d get on coming up the Beaulieu River in an America’s Cup 75 footer that does 50 knots of speed but one day we may give it a shout.

“I enjoyed sailing with Mary, learning more about the Beaulieu River and Buckler’s Hard and being back in a small scow without the pressure of competing at speed. In years to come, I hope to have more time to use the ‘freedom of the river’ on the water here. It is a huge honour to have been given the ‘freedom of the river’ when the two previous sailors to be granted it were Sir Chay Blyth and Sir Francis Chichester.”

Sir Chay Blyth said: “It is hard to believe that I came here 50 years ago as a young boy and have now returned as an old man. Nothing has changed really – it is still a fabulous place to come. It was a privilege to be asked to perform the original opening and I am glad that in my lifetime, the Beaulieu River has kept its charm and is as special today as it was during my first visit. I am proud to be part of these celebrations to mark such a major new milestone.”

The harbour’s redevelopment was carried out over two winters and included an additional 66 berths, larger berths for vessels up to 20m, upgraded electrical services, improved WiFi and a new dedicated visitor area. The work was carried out in consultation with Natural England and the Environment Agency to continue to protect the river’s unique habitats and species.

Lord Montagu said: “This investment is an important one in the river’s evolution, but it does not end here. With the water-based facilities now renewed, we will next be turning our attention to improved systems for the launching, lifting, moving and storage of boats. After that, we will be looking to upgrade our land-based facilities, the plans for which are already underway.”