That's a great set of hallmarks, Harold, and Ron has hit it on the button yet again
The marks are for Chester 1797, and the casemaker is John Ellison of Liverpool, who was known to be working between 1794 and 1808. Given also that yours is a pair case (which would make a recase even more unusual than normal, I think), you can be pretty sure this is the original case and therefore your watch is dated 1797.