“You have to try the sandwiches,” my colleague Lisa Markwell, the editor of The Telegraph Magazine, counselled when I casually mentioned I’d been invited to a garden party at Buckingham Palace to celebrate the UK’s creative industries.

“I’m not eating UPFs,” I heard myself saying (not my fault – blame Prof Tim Spector). “Is there a cloakroom?” I added. “They’re saying flat shoes on the emails. Mind you, everyone wears heels in the YouTube videos I’ve been watching since the invitation arrived. So maybe heels to start, then a change of footwear midway?”

“Don’t be ridiculous,” she said (to my point about UPFs), “the sandwiches are excellent. And no cloakrooms.” There are 775 rooms in Buckingham Palace, apparently. No cloakrooms for the 4,000 guests expected today? This is a relatively small garden party, by the way.

There are six held annually everywhere between London and Holyrood. In the course of these, according to the office of Really Important Statistics, 27,000 cups of tea, 20,000 sandwiches and 20,000 slices of cake are consumed …at each party. In case you’re wondering about the correlation with Britain’s soaring obesity crisis… No. Normally there are 8,000 guests at each party, so that’s a mere 2.5 sandwiches each and 2.5 slices of cake. 

Gates open at 3pm and guests begin streaming in, syphoned towards the archway on the far right as you face the palace, through to the gardens. To the left, a rather ugly temporary erection – Portaloos? Security hold-out? To the right, a military band plays a hotchpotch of film classics and 40 acres of immaculate verdant lawn, trees, beds and a lake. This is the largest private garden in the world – far bigger than the north London park I used to live opposite.

Nothing, not even that documentary starring the late Queen and Sir David Attenborough, prepares you for how large the gardens are. Someone had told me they were a bit municipal-looking, but the lake (I wasn’t expecting a lake), the willows… Can you imagine a back garden that can comfortably swallow 4,000-8,000 people and their hats? There are marquees dotted on the grass and vast groups of chairs splayed out like packs of cards. Guests are officially encouraged to explore the recesses, wander down the less traversed lanes, but no one wants to miss the grand entrance of our hosts.