A secret millionaire has purchased tickets to the tune of £100,000 ($146,250) for the biggest street party ever seen on The Mall to celebrate the Queen's 90th birthday. As charities were left at a loss on how to acquire tickets at a cost of £150 per person, the rich benefactor came to the rescue, buying hundreds of unsold seats on condition of anonymity.

"A donor approached Buckingham Palace saying they wanted to donate a number of tickets anonymously," an unnamed source told the Daily Mail. "The Palace approached the Patron's Lunch organisers to see if they could help facilitate this and then wrote to the 600-plus organisations and charities involved in the event to let them know about the generous offer and the tickets were allocated."

Queen Elizabeth II, the Duke and Duchess of Cambridge and Prince Harry are scheduled to attend the Patron's Lunch on 12 June to celebrate the British monarch's patronage of over 600 charities and organisations worldwide. The event was organised by the Queen's grandson, Peter Phillips, who initially said that only 1,000 of the 10,000 tickets would be made available to the public, with the rest earmarked for the Queen's charities, including Cancer Research UK, Action For Children, Barnardo's and the British Red Cross.

The number of tickets available to the public has now risen to 2,500, despite the donor's intervention. The precise number of tickets bought by the benefactor has not been disclosed, but up to 750 seats are known to have been purchased for charities, according to the newspaper.

"We are delighted that a number of tickets have been provided to patron's organisations by a third-party donor," a Patron's Lunch spokesman said.

Questions have surfaced over why organisations supported by the head of state should have to pay in order to attend an official royal celebration of their role.

The truly "Great British" celebration is being organised by global events company, Sports and Entertainment Ltd (SEL) for an undisclosed fee and charities were informed they could auction up to 40% of their share to raise the money for staff to be able to attend. Phillips is a director of SEL.

In February, Phillips stood down from his position as trustee of the Patron's Fund, which will distribute surplus money from the birthday event to support specific initiatives and projects run by the Queen's charities.

Explaining his decision at the time, a spokeswoman for the Patron's Lunch said: "It was… always Mr Phillips's intention to step down as a trustee once the Patron's Fund was fully operational to ensure that there was no perceived conflict of interest and to ensure the integrity of the event and the charity were maintained."