However, upon arriving home he looked the substance up on the internet.
On doing so, unemployed Mr Willman discovered the substance is likely to be ambergris -- a lump of sperm whale vomit -- which is used in perfumes such as Chanel No5 to amplify the scent.
The lump of vomit is often called 'floating gold' and is said to smell like old wood or fungus.
"It was like walking on the beach and finding a bag of £50,000 in cash," Mr Willman said.
A French dealer has already offered him €50,000, but it is believed that it could be worth twice as much as that.
Ambergris is the intestinal slurry of a sperm whale which is usually ejected into the ocean when the animal has a stomach or throat problem.