The fantastic golden leaves on the trees in autumn.
So reluctant are people to wave goodbye to summer fun, that next weekend more than 138,000 revellers will dress up as wrens, land girls, RAF pilots and teddy boys at the Goodwood Revival in Sussex. The vintage motor-racing festival, which falls a week after schools have gone back, is, according to etiquette guide Debrett's, proof that the "season" now extends into the autumn.
"Traditionally, the summer season used to take place from May until the Glorious Twelfth in August, which marks the beginning of the shooting season," explains Liz Wyse, etiquette adviser for Debrett's. "But now the season has cut loose from its origins; people are determined to keep partying throughout September."
But now the season has cut loose from its origins; people are determined to keep partying throughout September.
And why not? Lord March, who has been hosting the Goodwood Revival since 1998, regularly finds the weather to be much more pleasant than it is at the Goodwood Festival of Speed in June. Among those who have enjoyed balmy September weekends watching vintage vehicles and eating fish and chips wrapped in Fifties newspaper are David Cameron, Buzz Aldrin and Nigella Lawson.
Next weekend Rowan Atkinson will be racing an '80s Jaguar Saloon Mark 7 [it looks a bit like a beached whale, according to a spokesman for Goodwood], and Nick Mason, James Martin, Ewan McGregor and Katie Melua will be waving from the stands. "Everyone has been on holiday but now they're all back and are looking for some fun," says Lord March. "In the past fortnight we've almost sold out of tickets."
There has always been a scattering of social gatherings in September. The Flat racing season doesn't wind up until November and for the past 100 years the Royal County of Berkshire Show - the last county show of the season - has been held on the second weekend of the month: a great opportunity to pick up bargain country attire and early Christmas presents as the trade stands pack up for the last time before winter.
Meanwhile, over in Ireland, the Galway Oyster Festival, which was established by a canny hotelier in 1952 as a means of lengthening the season, draws in more than 20,000 oyster lovers each year.
But, over the past 20 years, a new guard of fixtures has appeared on the early autumn calendar: Along with the Goodwood Revival, which was first held in September purely to fit in with the grand prix season, there is Henley Literary Festival, and an army of food festivals including Ludlow [which celebrates its 18th anniversary this weekend], Abergavenny next weekend, York and Stratford-upon-Avon.
"There are practical reasons why Ludlow is held in September. Not only is it harvest, but there would be a danger of the food melting if we took place in July," says Beth Heath of Ludlow Food Festival.
In comparison with those fixtures held before August 12, events at this time of year tend to have a less formal, "end of summer" frivolity to them, according to Wyse. "The strict dress codes you find at Ascot and Henley are behind you," she says. "It's all about fun."
That's not to say people don't make an effort with what they wear. At the Galway Oyster Festival, ladies traditionally wear hats and dresses, and the younger generations are being encouraged to wear colourful masks when they take to the streets for a Mardi Gras parade on the Saturday night, while the Goodwood Revival attracts some of the most flamboyant outfits of the whole season.
Since 2010, when Lord March introduced a '40s, '50s and '60s dress code, the vintage motor-racing festival has also become one of Europe's most important vintage fashion festivals, with more than 80 per cent of visitors wearing costumes.
"It was originally just the architecture around the course that was in period style, then we started running the cars in an authentic way, and eventually we decided to go the whole way and get the staff and racegoers to dress up," says Lord March, whose natty collection of '50s and '60s suits features a particularly loud Prince of Wales-check suit and a teddy boy tweed coat. "A lot of people didn't think it was a good idea at first but when they saw how fantastic it looks with everyone in vintage clothing, they changed their minds. People behave differently in costume; they feel as if they're participating in making the weekend what it is."
After the Revival, Lord March admits that he goes into hibernation for the winter, reappearing only for the last Flat racing events of the season. But what of all these other mad festival-goers? According to Wyse, most of them will have settled down by the end of September, but for those who refuse to put away their suitcases, there's always Oktoberfest in Munich.
The Goodwood Revival takes place from September 14 to 16 and tickets are still available for Friday, September 14, costing pounds 36 for adults aged 22 and over, pounds 18 for those aged13 to 21; children under 13 are admitted free.
The September Season
Blenheim Horse Trials this weekend. Online booking has closed, but you can buy tickets at the gate (£24 Saturday, £16 Sunday, under 12s free)
Ludlow Food Festival also this weekend
Royal County of Berkshire Show: September 15-16
St Leger Festival Doncaster, September 12-15
Abergavenny Food Festival, September 15-16
Henley Literary Festival, September 24-30
Galway International Oyster Festival, September 28-30
Oktoberfest, September 22-October 7
The Daily Telegraph