Hi Janice, that *is* pretty! I love Rosina china - I have a whole load of cups and saucers (every one different) which get used when my parents are over as they like nice cups and saucers (not mugs!!!)
Mine are much later than yours though (mine = 1980s) - the backstamp on yours is shown as 1948+ in Godden's Pottery & Porcelain Marks. From 1952+ two other marks are shown so I guess that pins yours down to that sort of era. Rosina China Co started in 1941 but between then and 1946 they were George Warrilow and used different marks entirely.
Your pattern no isn't listed at Replacements.com but the pattern #4859 before it is shown... it has the same shaped cup as yours - link for interest:
http://www.replacements.com/webquote/RIA4859.htm - your flowers look like they could be lilies.
