You need two permissions to access Horsey Island: one from the farmer, the second from the tide, which offers a four-hour window in every 12 when the causeway can be crossed. It takes me 20 minutes to pick my way over, wading the deeper sections where spindly marker posts show the way. It’s a disconcerting place to loiter. In places the mud either side is a foot higher than the track, and riddled with tiny creeks in which streamers of sea forsaken by the tide rush along invisible gradients. The whole expanse fizzes and trickles as air and water try to escape from the mud and heaps of bladderwrack.

The dreamlike quality is enhanced by a feeling I’ve been here before, which, in a way, I have. The island is the setting for Secret Water, part of Arthur Ransome’s Swallows and Amazons series, which I loved as a child and revisited ad nauseam during a phase when my son read almost nothing else. It is here on the River Wade that two of the adventurous children are trapped by rising water and rescued by a marsh-wise local boy nicknamed the Mastodon, because of the enormous round tracks left by his “splatchers” – like snowshoes for traversing mud.

Horsey is home to a family of four humans, five dogs, a few hundred sheep, some visiting cattle and thousands of birds. Right now there are nests everywhere: swallows in the farmhouse sunroom; skylarks, lapwings and oystercatchers in the pastures; avocet, redshank and black-headed gulls on tiny islets in the scrapes and ponds. Scanning a human-made shingle beach on the island’s eastern edge from the farm pickup, we spot newly hatched little terns pootling about like downy pompoms escaped from a craft basket.

Joe and Vicky Backhouse steward these salty acres with care. Wildflowers are flourishing where the sheep are excluded and an innovative project is under way using 50,000 cubic metres of mud dredged from Felixstowe port to raise a dwindling area of marsh that was suffering from overgrazing – not by sheep, but the thousands of geese that arrive every winter. “We use less than 1% of dredged mud for any beneficial purpose. In Spain they use 90%,” Joe says. As sea levels rise, this little swatch of England is rising too.