The hostess was in jeans - imagine!

Theatre

Let's start with opera. Opera's quite posh, innit? They must have some reassuringly solid guidelines. "Actually, we don't," responds the plummy press officer for Covent Garden's Royal Opera House. "People can wear what they like." Even if I was wearing smelly Birkenstocks, ripped shorts and a bag on my back as big as a soprano, you'd let me in? "Um, OK."

"We hope men will wear DJs and women will wear dresses, but there are no codes," says the spokeswoman for Glyndebourne, which is about as posh as opera gets. Sounds as if opera is more relaxed than I had thought. "Oh, yes! Women even wear trousers here! Ladies! In trousers!" Surely not.

Populist theatre is a more complex proposition. Take Mamma Mia! at the Prince Edward theatre in London. If you think this would be just a casual night out for you and the rest of the American tourists in town, you're headed for a fashion faux pas on a Fergie scale. "People get dressed up, particularly on the weekends. Lots of Lycra," says Tom Littlechild, account executive for the show. "Seventies gear, you see." Philip Tuten, the theatre house manager, passes on the hot fashion tip that "lots of the ladies come in big wigs."

Court

Courts seem to have pretty fixed ideas about what is and isn't appropriate dress. "No, we don't have a dresscode," says the Old Bailey's spokeswoman. "I've seen jurors in shorts. A bikini probably wouldn't be appropriate, but it's really up to the judge." In the public gallery, anything goes ("We don't have any jurisdiction up there."), although layers should be avoided because "someone might think you're concealing a bomb". What if you're up in the dock? "If the accused is standing there in tattered jeans and a smelly T-shirt, that might not work. I would recommend smart casual." Funny, I had always thought "smart casual" was a criminal offence.

Dinner parties

"Oh, I just hate smart casual!" expostulates networking queen, Carole Stone, who, fortunately, does not have any immediate plans to be up in court. She does, however, have many dinner parties: "I had one for three couples - no, I can't divulge any names, but you'd recognise them," she begins. "One woman came wearing bunny ears and fairy wings, another wore a brocade train, and the third wore a skirt and cardie. No one felt uncomfortable!"

Stone speaks of a whirlwind world where ladies can "whip fine brooches out of their pockets to smarten up" and gentlemen can "rip off their neckties, when they're feeling overly formal." She also suggests "dressing down when in doubt". "Once I was going to a regatta and I felt underdressed, so I bought a £400 jacket on the way. But when I got there, the hostess was wearing jeans! Can you imagine?" No, Carole, I can't.

Religion

Lost in a swirl of foggy advice, where to turn but to one's rabbi? "Why, hi, Hadley, we haven't seen you round here for a while!" says Rabbi Mark Winer at West London Synagogue. Any old ways, next time I, ahem, come to synagogue, what would be appropriate dress? "Modest and proper," are Winer's bywords, which translates to a dress for women and jacket for men. Displaying an almost Diana Vreeland-esque talent at fashion planning, Winer suggests: "If it's a wedding and there's an event afterwards, wear your smart outfit to the ceremony. But really, we're so glad when people come we don't mind what they wear."

Moving swiftly on, what do the Catholics have to say? At Our Lady Queen of Peace in Bournemouth, people tend to be "reasonably dressed, although we do see shorts in the summer," says the housekeeper.

Is the C of E more prescriptive? "No, we're very relaxed," chirrups Dr Martin Dudley, rector of St Bartholomew's church, in the City of London. No rules at all? "We don't allow men to wear hats - except if they're builders and they're doing some works for us."

Sport

Perhaps sport is now the opiate of the masses, so maybe it is to the stadiums insteads of temples that we should turn for guiding light. "Nope, all very casual round here, not head-to-toe designer," says the press officer for Fulham Football Club. Should the light of heaven shine and you are invited into the corporate box at Fulham, don "jeans, jackets, smart shoes". Is this, by any chance... "Yes. Smart casual." The All England Club advises that Wimbledon spectators should "just be reasonably dressed and enjoy the game. I can't understand what else you want to know."

The Marylebone Cricket Club is more specific. "We don't allow any musical instruments and flags at Lords," says the MCC. "If you were sitting next to someone with a French horn, why, your enjoyment of the cricket match would be ruined! Flags obscure people's view, and it's the same with mock Viking hats, which seem to be quite the fashion item in certain quarters."

First-class air travel

A judge this week dismissed a juror for wearing an FCUK T-shirt. But what is appropriate dress in court? And while we're at it, what should you wear in a few other places? Hadley Freeman made some calls

"If you want to be bumped up to first class, dress formally," advises British Airways. "Skirt or trousers for women, jacket and trousers for men." If you aren't a blagger and actually fork out £6,000 for a first class seat you are "allowed to wear whatever you like".

The bank manager

Let's ask my bank manager for his opinions on appropriate dress - his views tend to be hard and unswerving. So, Mr Browne, what is appropriate to wear to a meeting with one's bank manager? "Oh, Miss Freeman, what have you done now, eh?" But Mr Browne does indeed have some views. "Best to look smart. As long as it's not offensive you should be fine."

Does he find "FCUK" offensive? "Well, a French Connection shop is right next door to us, so it wouldn't be very sensible if I did, would it?"