See Castle Street East 1 to 15 &c in London Addresses dataset
No 5 Castle St East Land Tax 1784 Charles Spragg / SunFire 1781 Charles Spragg gent, 5 Castle St, Newman St
The only Charles Spragg I found was a comedian (i.e. actor) who fathered an illegitimate child in Manchester, date not given but between 1773 and 1794. (Thomas Battye's Red Basil Book). Not in Highfill, Burnim & Langhans Dictionary of Actors etc.