Research by accountancy group UHY Hacker Young found that 35.8 million gallons of sparkling wine was sold last year, an increase of 5% on the previous 12 months.
But the increase was the smallest since 2011, amid a rising cost of imports from Italy and France because of the weakness of the pound, the report said.
UHY Hacker Young suggested prosecco may be suffering from brand overexposure through overstocking at supermarkets.
“A 5% increase in sales is not at all bad but that comes after several years of double-digit growth,” spokesman James Simmonds said.
“Unless the industry can revitalise its image this year, we may now be reaching ‘peak prosecco’.
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“It is hard for a luxury product to make the leap into the mass market without losing its reputation for exclusivity.
“A lot of English wine producers are now vying to capture the space left, as prosecco moves to the mainstream.”