Warmington-on-Sea (I thought 'Walmington' myself) is definitely described as a town on the South Coast. It has a pier and a lighthouse. I'd assumed Hastings, but the Kent connection is pretty specific, so over the border seems most likely.
As for a well-mapped area, Francis Brett Young's 'Far Forest' novels fictionalise the area West and South West of the Birmingham conurbation to the Welsh borders. I believe there is somewhere on the interwebs there exists (or did, back in the day) a list of corresponding towns, villages and other features.
The Wizard of Whirlaw was one of William Holt's books set in Calderdale - specifically Todmorden, in that case. I can't recall the others.
There is another layer, though: Real places in fictional contexts. I think of After London, by Richard Jeffries, or War of the Worlds, by HG Wells, which is pretty specific about locations. His History of Mr Polly and Kipps have some obvious markers.
As a fan of the Raffles books, I have looked into the locations used, many of which are real, and a few lightly fictionalised. I even began to plan a ride based around a particular story (notably involving bikes).