There are two different watermark options for this stamp - Crown CC or Crown CA. So you need to check the watermark. See the images below to see what they look like.
The Crown CC is Gibbons 28 or 28a (Rose or Dull Rose), Scott 9 - used value is about 35 Pounds.
The Crown CA is Gibbons 32, 32a (Rose-Lake or Rose-Pink) Scott 36 or 36a - used value is 32 Pounds;
or 33, 33a (Carmine or Aniline Carmine), Scott 36 used value is 2.75 Pounds.
Statistically, you probably have Scott 36, and if so based on the condition which is not excellent - it would not be worth more than $1.