Thanks for the excellent photos, I can see exactly what you have now.
This boldly painted 'flow blue' porcelain plate is marked for the Staffordshire firm of ***** ***** & Sons and this mark was used from c.1874 to 1924. The Art Nouveau style design -hand painted sprays of roses and rose buds & leaves- is a pattern called "Adams Rose"- and would therefore place it right in the middle of that range, circa 1890 - 1910 when this pattern was in fashion, itself a revival of an earlier, so called "stick spatter" decoration, that was fashionable in Regency England of the early 1800s.
Looking at the mark, what you describe as a lion or a vine leaf is, in fact, a monogramme of the initials GJ (for ***** *****) and the & Sons part is written inside the crescent. It's not very legible, so I sympathize with you not being able to identify it The impression has filled with glaze obscuring the details. Here's a slightly better image of what the mark should look like. The "B" and the "10" are factory codes for the type of clay body and mold shapes, etc, and can be ignored.
"Flow blue" is usually defined as being a china decoration where the edge of the blue bleeds into the white and is also often (but not always) created by using transfer prints rather than by hand painting. In this case it's the less usual hand painting and that elevates it from the ordinary.
***** ***** was considered one of the more artistic potteries operating at the time, and they produced a number of hand painted variations of the "Adams Roses" pattern. Here's their more usual one in colors. Your all-blue version is rarer.
As for value, if you saw your plate for sale in a retail setting, such as an antique shop, say, it would have a price tag of around £55. This is also the replacement value for insurance purposes.
Expect 30% - 40% of this if you were to sell at a good antique auction house or on line (eBay etc).
I do hope this helps!