[bryanrasmussen]

In most of human history there has been wider differentiation between the classes than there has been in the past 30 years or so, and as such there is unlikely to be just one uniform that allows authoritative access to every where, in most cases you will want a number of costumes suited to what you are attempting to do.

In 1880s London prepare an upper class costume as already suggested, a copper's outfit - this will also allow you to bear a formidable truncheon, it is nice to have access to weaponry when getting access to places when someone discovers you have gained access to said places.

[bryanrasmussen]

In most civilizations before reformation era Europe you would be best off dressing as some sort of priest or scribe.