Fundamentally, the show is about the uncertainty that the British people felt as their society changes. Mrs. Boyle laments how it's impossible to find servants because the lower-class don't know their place. Trotter comments that couples frequently find they've married a stranger because their families no longer check on the background of a partner. Christopher Wren is an effeminate young man who contrasts the very masculine Ms. Casewell.
There's more, but TV Tropes Is Not Spoiling This Ending