A couple of months ago, my daughter and her friend were at our house. I had found an address for writing to the Queen of England and suggested that my daughter and her friend write a letter. They both did, we mailed them and mostly forgot about them. Until today, when we received a Royal Letter in the mail. This was so fun for my daughter. It was a reply from a lady in waiting as the queen was unable to reply. They sent several interesting brochures with the letter with interesting facts about Buckingham Palace, the Queen and Royal Pets.
The picture is also a link to the official website. Here is also the address:
You can write to Her Majesty at the following address:
Her Majesty The Queen
London SW1A 1AA
If you wish to write a formal letter, you can open with 'Madam' and close the letter with the form 'I have the honour to be, Madam, Your Majesty's humble and obedient servant'.
This traditional approach is by no means obligatory. You should feel free to write in whatever style you feel comfortable.