Mr Thomas said was "unlike any I'd seen before" and came from a lone old apple tree in the hedgerow with a large number of fruit on it.
Apple trees grown from seed are all different, so cultivated varieties, or cultivars, are propagated by taking cuttings from existing trees and grafting them onto rootstock to ensure the new tree and its apples are the same.
Apples have been cultivated in this or similar ways for thousands of years.
Mr Thomas, who works for wild plant and fungi conservation charity Plantlife, was keen to identify the unusual apple he had found in a little-visited spot - to see if it was a known cultivar, or a new variety he could name himself.
"While I am certainly no fruit expert it immediately struck me as highly unusual, unlike any apple I'd seen before," he said.
"Excited by the pale and mottled oddity, I set about trying to get it identified with a view to perhaps one day being able to name it.
"That was the dream, but I did half suspect it would turn out to be something much less exciting than it is."
After what he describes as a "wild apple chase", with many fruit experts flummoxed by the find, he received help from Plantlife colleagues and was then pointed towards the Royal Horticultural Society fruit identification service at RHS Wisley.
RHS fruit specialist Jim Arbury inspected three of the apples and informed Mr Thomas it was not a planted cultivar, but a new variety which he could propagate and name.
Mr Arbury said it was "a very interesting apple".
It is clearly not a planted tree, but a seedling that could be a cross between a cultivated apple and a wild Malus sylvestris, a European crab apple, he said.
"It tastes quite good. It's a cooking apple or dual purpose, you can eat it, it's got a bit of acidity but it's got some flavour, and some tannin, which is what you have in cider apples," he said, adding it could be used with other apples for cider.
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