Mr Brown caused a stir in the City when he declared he would be wearing a lounge suit, rather than the black tie stipulated on invitations to the dinner, to deliver his speech to the gathering of bankers and merchants. But a secret meeting of City fathers concluded last week that it would be inappropriate to undermine further a dinner which was only recently downgraded from white tie to black tie.
However, Mr Brown won't be turned away. "We are not sending out a note saying specifically that black tie is optional, but if anyone phones and asks about dress code, we will assure them that they will not be refused admission if they are wearing a lounge suit," a Corporation of London spokesman said.
This tough line compares with the cave-in at the CBI, which had originally stipulated black tie for last week's annual dinner in London. However, the Chancellor's insistence that he wanted to wear a lounge suit prompted a hasty restatement of evening wear guidelines.
Guests were informed by phone that black tie was optional. And to reinforce their desire to make Mr Brown feel at home, all guests on the CBI's top table wore lounge suits. The majority of diners, however, stuck with black tie.
According to the comedian and impressionist Rory Bremner, who spoke at the CBI dinner, if Mr Brown is not careful he will begin to make his predecessor Kenneth Clarke look like a snappy dresser.