OG & David - Something was nagging me about the crown from my stamp collecting days (long ago), so I looked it up. What is on the Webb mark is the Tudor crown. Queen Elizabeth (I will avoid her full title so as not to cause strife north of the border) was crowned with St. Edward's crown, which has a depressed top. Why, I hear you ask, when all previous monarchs were crowned with the Tudor crown? Apparently the change was made to mark the fact that Queen Elizabeth was not being crowned Empress of India, a title that her father lost in 1947 (also from 1948 you will notice that IND. IMP. is absent from our coinage). St. Edward's crown was also considerably lighter than the Tudor crown, making it easier for the Queen to wear.
So the coronation being commemorated by your goblet has to be that of George VI on 12 May 1937.
... yet another example of a souvenir being produced with an incomplete or even missing inscription that was unnecessary at the time as everyone knew what it was for, but which has caused problems many years on. See also the Greener pressed glass souvenirs that appear to celebrate a visit to Nova Scotia by the Marquis and Marchioness of Lorne in 1878, but which actually celebrated Princess Louise taking up residence in Canada, something obvious to everyone at the time. There is an early engraved glass in one of the books that is now a complete mystery that also falls into this category, as possibly does the fort series of table centres by Molineaux & Webb, Rd. No. 29780.