This a lovely flow blue Staffordshire pot de creme cup in the Nankin pattern by R. Stevenson. The set includes the cup with matching lid and a matching saucer. Staffordshire porcelain (England) is famous and dates back to the 1700's. You may have see the famous porcelain dogs which are copied everywhere now. This pot de creme cup and saucer was produced prior to 1836.
Flow blue refers to the style of the glaze that gives the pattern a slightly blurry appearances. You can use that link to learn more about flow blue. There are many collectors of this beautiful porcelain.
Ralph Stevenson was born in 1776 in Burslem Staffordshire, England. He went into the porcelain manufacturing business in 1800. He had various partners and produced a lot of good porcelain. His last factory closed in 1836. He had an interesting history and you can read more about Ralph Stevenson here.
Unfortunately we don't have an image of the pottery mark but the R.Stevenson pieces were all marked.