Printed between 1855 - 1857. The S.G. Catalog number is #62,#63,#64,#65,#66 depending on watermark and paper type.
Three watermarks are possible... Small Garter (2.7 million stamps), Medium Garter (3.6 million stamps) and Large Garter (28.7 million stamps).
Chances suggest you will have the large garter watermark but check as values vary with watermark and paper types with catalog used value from £120 UK to £1000 UK.
Spotted the LG watermark variety on
ebay recently ... 15 stamps for £105 UK