I think all pictures posted so far (except Geoff's) are of Richard's Pipits.
Geoff's picture shows a classic Upland Pipit for comparison.
I agree that call is the easiest way to separate the two species (and cetainly the easiest way to find upland pipit) but structure is also important. Upland has an odd structure, not very pipit-like; it is fairly short-legged and the bill is shortand deep, seemingly continuous with the line of the crown, and often held at a slight upward angle (as shown on Geoff's photo). Upperparts are evenly, narrowly streaked, underparts are fairly unmarked (with some narrow streaks) and there is little sign of a malar.
One confusion here is that the race of Richard's Pipit breeding in HK is sinensis, whereas most birds in winter are of the richardi race. Sinensis is slightly smaller and heavier-billed, and is more heavily streaked on the back (but with thicker streaks than seems to be the case for Upland)
A further confusion now is the presence of juvenile birds, which can appear to have heavier bills than adults. Kitty's picture shows a juvenile Richard's Pipit - note the long legs, heavily marked upperparts and obvious malar. Aging the bird as a juvenile is easy based on the pronounced 'scalloping' of the upperparts, created by dark centres to each feather.
