Last year Kenneth Clarke started the rot at Mansion House when he abandoned the 120-year-old dress code of white tie, a complicated affair of bibs and studs, in favour of the black-tie "French waiter" look.
Now his successor, Gordon Brown, has let it be known that he will be wearing a bank manager-style lounge suit.
I am told that Mr Brown always wears exactly the same thing - dark blue suit, blue shirt, red tie with white spots on it and black shoes (no Clarke- style Hush Puppies nonsense).
New Labour insiders speculate that he once bought a job-lot of them to save time.
Alderman Cork will be wearing his full bib and tucker, whatever anyone else turns up in. But it could be said that past Lord Mayors could have contributed to this modern malaise.
Back in the 18th century Sir William Curtis MP, known as "Billy Biscuit" because of his Bermondsey naval biscuits factory, was mercilessly lampooned for his absurd get-ups.
A collection of George Cruickshank's cartoons of our Billy, illustrated here in an imaginary costume, goes on show at the Guildhall Library next week.
Back to today. The Treasury is sanguine about the current flight from formality at Mansion House, but the City Corporation is a little more concerned.
A spokesman says: "Will it be T-shirts and flip-flops next year? I'm not sure that we have ever seen anyone in T-shirt and jeans at this occasion. On the other hand we're not in the business of chucking people out."
Everyone's talking about That Dinner. You know the one, on 10 April, when George Bull, chairman of GrandMet, invited his opposite number at Guinness for a spot of dinner. By the time the liqueurs came they had decided on a pounds 20bn merger.
According to Mr Bull, the confidential tete-a-tete in central London was a jovial affair. "We have been friends for years," he says.
"Tony Greener and I have known each other for 17 years and have been in 'friendly conflict' with each other across the world, and therefore it's a matter of great pleasure now to come together.
"The discussions started because I invited Tony to dinner," says Mr Bull.
"It was exactly at that dinner on that date that I put the proposition that perhaps it was time that we settled down to a serious discussion and consider the prospect and the possibility."
Mr Greener then shot off for a week's holiday in Africa where he mulled the idea over, having instructed his underlings to figure out whether the regulators would allow the deal. They thought yes, and the rest is history.
Whether the merger was toasted with malt whisky, Mr Bull wouldn't say.
Granada and Yorkshire-Tyne Tees (YTT) are cosying up again, I hear, following Granada's recent frosty proclamation that it had "no present intention of bidding for YTT".
Granada already holds 27 per cent of YTT, and City punters are panting for a bit of bid action. But Granada recently broke off contact with the TV company as it thought YTT had been trying to "talk up" its bid price.
Then last week both Gerry Robinson, Granada's chairman, and Charles Allan, the company's chief executive, were spotted sitting in the front row of YTT's agm.
Taking valuable time off from their programme of selling off various hotels, messrs Robinson and Allan then shared the Forte corporate jet with Ward Thomas, YTT chairman, as they flew back from Leeds to London after the agm. The pipe of peace was smoked, and merger talks were resumed. Look out for a statement soon.
Evita lyricist Tim Rice and Yorkshire-born interviewer Michael Parkinson had the shine wiped off their weekend last Friday when Pavilion Books, a small publishing company of which they are both non-executive directors, went bust.
Happily the receivers, Keith Goodman and Philip Monjack of Leonard Curtis, managed to sell the business yesterday to another up-and-coming London publishing house, C&B Publishing.
Pavilion produces coffee-table books, mostly with a culinary bent.