The culmination this weekend at Castle Howard of the county’s date in the English summer social calendar threatens the kind of fashion faux pas that used to mark out one class from another – an eventuality that has led the organisers to issue an informal dress code this year.
It advises festival-goers especially that the event “does not lend itself to Glastonbury-style boho chic”.
Acknowledging the trend towards casual elegance, however, it comes down more on the side of wellies than white tie.
“When you look at the audience at indoor Proms concerts, smart seems to be the order of the day, but for our open air concert, there’s a far more flexible approach,” said Abbigail Ollive, at Castle Howard, where Brideshead Revisited was filmed and in whose wide-open grounds on Saturday, the operatic soprano Sarah Fox and tenor Wynne Evans will be accompanied by the London Gala Orchestra, conducted by Stephen Bell.
Ms Ollive said that while most of the expected 6,000 visitors would bring picnic blankets and deckchairs, some would dress up and bring linen tablecloths and even candelabra to set off their costumes.
The union flags associated with the last night of the London Proms are also encouraged at the Howardian version, but Ms Ollive cautioned that they should be of a sort suitable for a Royal wedding, not a Spice Girls costume.
Rachel Deighton, the event manager, said: “We’ve noticed over the past couple of years that as the picnics get more elaborate, so does the dress.
“We do get groups of people in evening gowns, but there will be couples next to them who are quite happy sitting on their picnic blankets in their Hunter wellies.”
The venue, near York, was one of the first outside the South to embrace open-air concerts, more than 25 years ago, but the resurgence of interest in hearing the classics means it no longer has the market to itself.
“But it has special place in people’s hearts, and that’s just down to the setting,” Ms Deighton said.
“Sat in front of the house on the lawn, looking over the lake and listening to world class musicians paying – it doesn’t get any better to that.”
Unlike Glynebourne, the East Sussex manor with its own opera house, whose festival has been running from May to August since before the war, Castle Howard has no written dress policy. The Glynebourne founder, John Christie, encouraged the wearing of formal dress “to show respect to the singers and musicians”.
However, the two venues have in common the advice to bring an additional warm layer to combat the chilly evenings and the odd spot of rain.
“Whilst a shirt or standard top might be perfectly adequate for picnicking, once the sun sets, the temperature does fall considerably,” Ms Ollive said.