The Prince of Wales is said to hope the nation does not return to “bickering” after the feeling of “togetherness” over the Platinum Jubilee weekend.
The couple mingled with the 450 guests who included people from a variety of organisations, as well as locals and a group of 70 volunteers from the Royal Voluntary Service.
Sarah Friar, CEO of neighbourhood app Nextdoor, was among those to meet Charles when he sat opposite her at her table.
“He said at the end how great it was that everyone comes together this weekend,” she said.
“We see it with neighbours, right? I’m from a company called Nextdoor, so people coming together with the best coming out.
“People who don’t know each other are out having fun.”
Ms Friar, who lives close to San Francisco but is originally from Sion Mills in Co Tyrone, said that Charles commented: “When it comes to Monday are we going to go back to all the bickering again? Let’s hope we don’t do that.”
Ms Friar said it was “a wonderful thought” for all of us.
Gemma Snow, from the Eden Project, was sitting next to Charles and said he talked about “keeping that togetherness going”.
Saturday night’s concert at Buckingham Palace came up in conversation too, with Ms Friar saying Charles described it as “marvellous”.
Local resident Sonia Wilson also mentioned the Party at the Palace to Charles.
“He said ‘I’m sorry to keep you from your lunch’. I said ‘No worries, I had my marmalade sandwich’,” she said.
Ms Wilson said Charles laughed and replied: “That’s a good joke, isn’t it?”
Singer Elaine Paige, ambassador for the Royal Voluntary Service, met Charles and Camilla at the lunch.
Speaking afterwards, Paige said: “I think that they are having a marvellous time. Obviously it’s quite a schedule for them all.
“But I think he seemed very relaxed and full of good humour, and I think his opening comment was – because it was only half past 11 – ‘It’s a little early for lunch’.”
Speaking about the Queen’s sketch with Paddington Bear, she said: “I thought to myself what a brilliant actor she is.”
She said the Queen had “perfect timing” and has a “twinkle in her eye”, adding: “I think she’s just the most superlative actor. It was brilliant. Absolutely brilliant.”
Charles and Camilla viewed a 6×1.5m tea-party themed felt art piece by Lucy Sparrow when they arrived at event at the cricket ground.
The piece will be displayed later this year in the Grand Entrance of Buckingham Palace.