Peter Phillips, the queen's eldest grandchild and son of Princess Anne, is organising the Patron's Lunch, which he said would have a ‘carnival atmosphere’.
The more than 600 charities and organisations of which the queen is patron will be able to buy 9,000 of the tickets and sell on up to 40 percent of them in fundraising events -- with the rest to be distributed among staff.
Next month, members of the public will be able to enter a ballot for the other 1,000 tickets.
The June 12 lunch on The Mall, the one-kilometre processional route to Buckingham Palace, will be attended by Queen Elizabeth and her husband Prince Philip, as well as their grandchildren Princes William and Harry.
Though 13th in line to the throne, Phillips, like his sister, the former eventing world champion Zara Tindall, has no royal title and does not undertake royal duties.
The 38-year-old runs the British arm of the Australian global events agency Sports and Entertainment Limited. He pitched the idea to Buckingham Palace.
‘We had to show that this wasn't a case of trying to cut corners because the queen happens to be my grandmother,’ he said.
Phillips defended the cost of the tickets, saying it was a not-for-profit event and any surplus would go to the charities.
‘It's not exactly a cheap exercise. Fortunately our corporate partners have provided the funding for the majority of the costs,’ he said.
But the British media took aim at the ticket cost.
‘It had better be good’ for that price, said The Times, which cited a public relations expert saying a free bash would have been better PR.
The Daily Mirror quoted Joe Little from Majesty Magazine saying he expected the pricing to attract ‘a lot of flak’ for tickets priced ‘at a level that would exclude an awful lot of people’.
Queen Elizabeth turns 90 on April 21, but British monarchs' official birthday celebrations are traditionally held in June -- the thinking being the UK summer weather ought to be better for outdoor celebrations.
The milestone will be marked with a service at Saint Paul's Cathedral in London on June 10, with the traditional birthday military parade the following day.