As St Paul's finally said: march up (5)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of D (‘finally sai D ‘) plus OMED, a reversal (‘up’ the down staircase) of DEMO (‘march’). Nothing to do with the answer, but in the course of investigating this clue, I discovered that the first recorded version of “ Oranges and Lemons ” does end with a reference to St. Paul’s.