The 65-year-old celebrity chef was attending the opening press day in the gardens of the Royal Chelsea Hospital when his sister, Jacqueline, fell head-first into a narrow water feature at the BBC Studios exhibition garden.
An eyewitness said Jacqueline appeared close to drowning and coughed up water after being dragged to safety by a group of people including her younger brother and DIY SOS presenter Nick Knowles.
Paramedics rushed to the scene to care for Jacqueline, who was later confirmed by Mr Harriott to be in better shape.
On Monday afternoon, Mr Harriott tweeted: “Just a big thank you to everyone who helped my sister when she had a fall at the Chelsea Flower Show this morning. She’s doing fine and all is well.”
Volunteers at the event, which is run by the Royal Horticultural Society (RHS), confirmed that they were planning to erect barriers around the feature to protect other attendees.
Eyewitnesses described seeing Jacqueline fall into the pond in the BBC Studios Our Green Planet and RHS Bee Garden. At the time, guests were not aware she was Mr Harriott’s sister.
One guest said: “The garden was packed with lots of people and I think the woman must have fallen into the pond or tripped over and ended up in the water.
“I think she nearly drowned. She was pulled out by Ainsley Harriott and some other celebrities before they laid her down on the floor. She was coughing up lots of water.”
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The garden is one of numerous displays that feature cutting edge techniques from world-renowned designers. The show is expected to attract thousands of visitors during its week-long run.
The BBC Studios garden describes itself as “inspiring garden lovers to play their part in balancing our ecosystems through planting and design that supports bees and all our wild pollinators, especially those currently in decline within the UK and beyond.”
The Chelsea Flower Show is back in its May slot for the first time since 2019, after being cancelled in 2020 and moved to September for 2021 due to the pandemic.
Gardens this year focus on wildlife, wellbeing and floral displays to mark the Platinum Jubilee.
Celebrities and members of the royal family are getting a first look at the Royal Horticultural Society’s showpiece event on Monday, before it opens to members of the public.
Among the show gardens is a recreation of a beaver wetland, complete with a beaver lodge, dam, streams and natural wildflower planting.
Additional reporting by agencies