Plymouth, Devonport and District Tramways
The Plymouth, Devonport and District Tramways company operated steam services for barely one month before a Devonport Corporation injunction prevented them from further running until such time as the entire system had been constructed, a situation which soon led to the company filing for bankruptcy. No photographs whatsoever have survived that depict the steam trams, let alone the staff who worked them, so it is impossible to know for certain whether or not uniforms were worn.
Perhaps more surprisingly, not a single photograph of the later horse era - operated by the Plymouth Tramways Company from 1899 to 1892 - has survived, so it is also unknown whether staff of that concern wore uniforms. However, given that the successor to the PTCo, Plymouth Corporation, did not see fit to issue uniforms, it seems more than likely that they merely followed existing practice, and that staff of the PTCo simply wore informal attire.
For a history of the company, see 'A History of the British Steam Tram Volume 4' by David Gladwin; Adam Gordon (2008).