The diversion to Fackenden Down is a great variation to the Shoreham circular walks. If you walk over the top of the hill and continue to Magpie Bottom you join the Romney Street walk, shortening it slightly. Fackenden Down and Magpie Bottom are both sites of special scientific interest and are examples of chalk upland being rewilded. Both have great biodiversity with rare plants, insects, birds and reptiles. See details (Walk 19). The other walk that can be altered to take in Fackenden Down is the ‘eastern valleys’ walk. Here are some pictures:
Here’s a map of the near-four-mile route; description here
Kent walks near London 