Cameron hails 'exciting' political party at Palace for Queen's 90th birthday
Prime Minister David Cameron said it was "very exciting" to mark the Queen's 90th birthday with an "array" of political figures at Buckingham Palace.
Representatives from both Houses of Parliament and from across the political spectrum attended the event.
But Labour leader Jeremy Corbyn, a noted republican who kicked off Labour's In For Britain EU campaign on Tuesday, missed the engagement.
He was attending a family funeral instead, and a Buckingham Palace spokesman said he had "personally written" to the Queen explaining his absence.
Wearing a blue and white floral day dress, the Queen, who has broken records with her 64-year reign, met the political figures from both the Lords and the Commons in the Palace's White Drawing Room.
Lords Speaker Baroness D'Souza and Commons Speaker John Bercow presented a Humble Address to the Queen on behalf of their respective Houses.
Speaking after the presentation, Mr Cameron noted that the gathering was a special occasion which does not happen very often.
"It is very exciting - I have been Prime Minister for six years and Leader of the Opposition for 10 and I haven't done anything like this," he said.
He said there was "quite an array" of political individuals in attendance and added that he is looking forward to the royal birthday celebrations in June which include a picnic on The Mall and Trooping The Colour.
"There has been an immense outpouring of respect and joy for her 90 years and everything she has done," he said.
"For so many of us she has been the only monarch that we have ever known and will ever know - that does make it very special."
Baroness D'Souza told the Queen in her Humble Address that the House of Lords offered their "heartfelt" congratulations on her becoming a nonagenarian.
"We all owe you a very large debt of gratitude for the extraordinary service that you given throughout your long career," she said.
Mr Bercow presented the address on behalf of his parliamentary colleagues from all parties within the Commons.
"You will recall that on several occasions we have publicly, and I think with force, expressed our admiration of a lifetime of service by you," he said.
He referenced the 29 members of parliament who stood up to offer their congratulations and who described the "extent of their reasons for their respect" for her.
"They spoke for themselves, for the House, they spoke for the country and for millions of people throughout the Commonwealth and indeed way beyond," he added.
The Queen then handed over a letter of reply to both speakers in response to their addresses, before she hosted a champagne reception for the guests - who were served crisps, pretzels and canapes of duck terrine and asparagus quiche.
Guests included the Archbishop of Canterbury Justin Welby, Angus Robertson of the SNP, Ukip's Douglas Carswell and Caroline Lucas of the Green Party, Lib Dem leader Tim Farron and shadow leader of the commons, Chris Bryant.
Lord Laming, Baroness Stowell, Baroness Smith and the Lord Hope of Craighead were among the other figures also in attendance.
Following the line-up, where Her Majesty had greeted guests beginning with the House of Lords, Baroness Stowell revealed the Queen had quipped: "We can all relax now."
The Queen's official birthday will be marked on June 11 with the Trooping the Colour event.