This is Joseph Machin's pattern 140, known to collectors as "The Proposal". It dates c 1810.

This well documented pattern can be seen on page 118 in the book "Machin Porcelains & Earthenwares" by Bill Thom and Philip Miller. The pattern is also shown on page 127 of "Chinoiserie" by Howard Davis. The teapot in this pattern is shown in "An Anthology of British Teapots", Miller and Berthoud, plate 1366, page 228. It is 6" high and about 11" long.

Both teapot and cover are in excellent condition. The only flaws I see are some wearing away of the over-glaze painted pattern, and a 1/8" shallow flake to the edge of the cover.