At last, after quite a few visits to the campsite over the last couple months I eventually connected with the two Water pipits before work this morning. There were around 18-20 pipits on the very flooded campsite, majority were Rock pipits with about 4 Meadow pipits. If approached too closely many would just fly from one side of the flood to the other, but there were 6 birds that disappeared high and away onto the marsh and out of sight.
Link to Water pipit id