A mystery.  What is the relevance of this flag today? Around here I have seen no decorations or even evidence of the Coronation taking place in London.  Then I saw this flag in a garden which frequently has the Union Jack or Saltire so guessed it must be raised by a Royalist supporter.   However on researching the flag it appears to be a copy of the 1694 to 1702  Royal Standard of King William III and II (William of Orange) who ruled jointly with his wife from 1689 till she died in 1694.
 “A banner of the Royal Coat of Arms of William III, first and fourth quarters representing England and the English claim to the French throne, second quarter representing Scotland, third quarter representing Ireland, with an inescutcheon for the House of Nassau.”