In the drawing room of Little Bentley Hall, plans are already being finalised for next year’s charity garden show. It may still be seven months away, but a British Army band from the Queen’s Division has already been booked to perform at a gala opening for an expected 800 guests.

Although the event has been a staple in the Essex social diary for some years, next year’s event could be more lavish than usual. For Little Bentley Hall’s proprietor, retired banker Christopher Palmer-Tomkinson, is about to share in one of the City’s biggest pay days.

Cazenove, the Queen’s stockbroker, is selling itself to an American banking giant in a £2 billion deal that brings down the curtain on 190 years of blue-blooded history.

As a result, a £650m-plus windfall will be shared between 80 Cazenove bankers past and present — including aristocrats and a network of Old Etonians. These 80 bankers own the bulk of the shares, with 25% owned by other staff and 10% by institutions.

Palmer-Tomkinson, 67, is typical of the breed: his brother skied with Prince Charles, while his niece is society “It Girl” Tara. He is in line for an estimated £10m to £12m, based on shareholder documents seen by The Sunday Times.

Bernard Cazenove, 62, the last member of the family to work for the firm, is expected to pick up more than £14m. He, too, has long since retired — along with many other big beneficiaries.

David Mayhew, meanwhile, Cazenove’s 69-year-old chairman whose name has become synonymous with the firm over the past 40 years, is expected to pick up as much as £20m (including the proceeds from recent share sales).

For many of the Cazenovians, it will be the biggest bonus they will have seen in 30 or 40 years. While American investment banks offered golden hellos and cash bonuses, Cazenove considered such things uncouth.

Now, five years after Cazenove placed its investment banking business in a joint venture with JP Morgan, the American giant is about to take up its option to buy the business outright in a deal that values it at about £2 billion.

While it was always expected that the original November 2004 agreement would ultimately see Cazenove sell up, it was never expected to happen like this.

However, the business is set for its biggest-ever year. Thanks to a combination of JP Morgan’s financial muscle and Cazenove’s adept handling of contacts, the JP Morgan Cazenove business has been involved in every big capital raising in the London market — from HSBC to Rio Tinto and Land Securities to Lloyds Banking Group’s current £13.5 billion rights issue.

The joint venture is on track to make record operating profits of about £500m this year — almost three times last year’s total. The option to sell to JP Morgan has come at an opportune moment.

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive