Thanks all for your help. I'm trying to find out this information for the son of a former minister of the chapel, who no longer lives in Leicester, but was clearly struck by the gravestone, because he recalls it from his schooldays in the 1950's. I would have to see the gravestone again, which I should hopefully be able to do before too long, to check that I am correct in remembering it as mentioning his death in Worksop. Unfortunately, though there is a reference to the gravestone on the Historic England website, there is no image online.
The gentleman interested in the headstone believes that Captain Spencer was on his way home from the American Revolutionary War, and he was certainly in the army at the right time. His PCC will says he was formerly in the 79th Regiment of Foot. However, by 1778 he was presumably serving with the Leicestershire Militia, because I've found this:
http://record-office-catalogue.leics.gov.uk/CalmView/Record.aspx?src=CalmView.Catalog&id=QS%2f67%2f1%2f5%2f30&pos=8There are further entries for 1779 and 1780, and he had been promoted to captain by the time of the 1779 record.
A couple of points I'd appreciate help with, if possible:
1) Do these records mean that Captain Spencer was present in the town of Leicester on these dates in 1778, 1779 and 1780?
2) Was the Leicestershire Militia the same thing as the Leicestershire Regiment, aka the 17th Regiment of Foot, which certainly seems to have had an illustrious role in the American war? My understanding of the Wikipedia entry for the Leicestershire Regiment suggests that it was not the same thing at that time. Was the militia more like a reserve unit?
If Captain Spencer did indeed die at Worksop (which, as far as I can see, was on the route of the Great North Road) then it suggests he may have been on some sort of service in the north of England (or even Scotland?) prior to dying "on his march home".
Dave