Meadow or Tree pipit?
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Not sure, really. The breast streaking looks more like Meadow, on reflection. Did you get any more photos of it? A pic of the hindclaw would help, for example.
My Flickr photos...
I'm afraid I have no other pictures, will consult some more ID books considering your comments and report back. Thank you very much!
Another factor to take into consideration is the habitat. Unless this is a passage migrant, and it's a bit early for that, than it would be seriously out of its usual home range if it was a tree pipit on a coastal path. However this is just the sort of place you would expect to find a meadow pipit. Personally I would wait until I hear it call. Meadow pipit gives a much softer squeak than tree pipit's harsh call.
(Coming in rather late here...)
I agree with Bob Ford: Tree Pipit is pretty much ruled out by the date. Meadow Pipit does breed in this locality and is by far the most likely species. However, you should also consider Rock Pipit, which also breeds locally, and occasionally appears on top of the cliffs rather than at the foot of them.
(I've been birding on Thanet for 40 years now and your bird is on my local patch!)
I don't want to prolong the issue, but it needs to be said that date is not at all a reason to preclude Tree Pipit. Non-breeding birds/failed breeders can turn up anywhere at any time and I have seen loads of Tree Pipits on passage in that general area in the past. It's certainly not a Rock Pipit, of course. I agree that Meadow is more likely, however. A tricky one.
Lat/Lng: 51.3892298, 1.4340766
OS grid ref: TR390711
Coastal grassland, cliff top