Prime Minister David Cameron (R) and his wife Samantha (2L) stand with Queen Elizabeth II and The Duke of Edinburgh (L) outside Number 10 Downing Street on June 21, 2011 in London, England.

The Camerons have invited the Duke of Edinburgh and The Queen to Downing Street to celebrate The Duke's 90th birthday.
http://www.dailymail.co.uk/news/article-2006330/David-Cameron-wife-Samantha-host-birthday-lunch-Prince-Philip-Queen.html