Selsey I think is both too large to count as a village and too far (remember it's supposed to have been a 5 mile diversion - not 7.5 miles - although if you consider distance as the crow flies from Chichester Marina it would be about 5 miles...). Also, Selsey's most notable resident by far is clearly Sir Patrick Moore the astronomer. Sidlesham is only 4.5 miles from the A286/B2201 road diversion at Kingsham, and approx. 3 miles by air from the Marina. The text is obviously a bit ambiguous about this. However there is a charming country inn (The Crab & Lobster) at Sidlesham, which would fit in well with a lunch stop. The historical info about King Ella is, truth be told, not helpful in deciding the location, and we are agreed that the net doesn't offer useful info linking John Baxter with either Selsey or Sidlesham. For me it must be the latter.