Princess Ida

 White background, scalloped rim, floral sprays with pink roses around rim.  c 1954.  It was originally produced in the 1930s and early pieces with a cream background still crop up from time to time.

A google search turns up the following info:
Princess Ida is a Gilbert and Sullivan theatrical production originally from 1880's. The Wikipedia site
shows that there was a production at the Savoy Theatre in 1954.
The large bubble/scalloped edge of the plate on this page indicates the plate was C1950, but the "BY" markings were thought to still be circulating mid 1950's. See Sharon's info on this page about BY markings
J & G Meakin are known to have named other china patterns after plays, novels, and films.
Large set of Princess Ida, courtesy Jake **note EGGCUPS lower right **