[Stooky Bill]

It was floated in July 1986, Thorn EMI and BET retained significant shareholdings (more than they had intended) after then until Pearson took over. If you look at late 1980s programmes you will see it had become “Thames Television plc” at that point (though re-registration as a plc does not definitively indicate a stock market listing, it is a prequiste to doing so).

They tried floating it in 1982 but were blocked by the IBA. Then EMI and BET almost sold the company to Carlton in 1985 but that was also  blocked by the IBA. 

The listing of Thames didn't go as well as Thorn and BET wanted - they wanted to have only a 28% stake, but ended up with 56%. They did try and sell Thames in 1990, with Carlton as a potential buyer but it didn't happen and they eventually sold to Pearson in 1994