Metropolitan Street Tramways Company
The Metropolitan Street Tramways Company opened for business on the 2nd May 1870, and by the end of that year, a new company - the London Tramways Company - had been formed to take it, and another South London concern, the Pimilco, Peckham and Greenwich Street Tramways Company, over. Although this was not formally achieved until 1873, it is believed that both it and the PP&GStTCo were operated as a single concern well before this date.
What is clear, is that images of the MStTCo taken during its earliest years appear not to have survived, so it is currently impossible to say whether or not staff wore uniforms. However, on the balance of probablity, and in view of the early policy of the London Tramways Company (see link), it seems likely that drivers and conductors wore smart, but informal attire.
For a history of the company, see 'London County Council Tramways Vol 1: South London' by E R Oakley; London Tramways History Group (1989).