The Official Charts Company confirmed the unusual statistic on its Twitter feed today (January 4).
"#OfficialChartFact: Sales of cassette singles, yes CASSETTE SINGLES, tripled in 2012 to ermm 604 units. Guess what the biggest seller was?" it teased.
"Two of you have guessed Mr Blobby. WRONG! Guess again.
"Clue 2. 2012's biggest selling cassette single WASN'T Rik Waller, Michelle McManus, Fast Food Rockers, or Thomas The Tank audio book."
It added: "Neither was it Lisa Scott-Lee's - TOO FAR GONE.
"Sorry to disappoint hopeful Rachel Stevens fans but#OfficialChartFact: Biggest selling cassette single of 2012 was Border by @FeederHQ."
'Borders' by Feeder - released this year on CD, cassette and 7" - was taken from the band's last album Generation Freakshow.
It was the first cassette single released by the band since 'Just a Day' in 2001.
The Official Charts website later confirmed that 'Borders' had sold 480 copies, accounting for 80% of the UK cassette singles market.
Watch the Feeder 'Borders' music video below: