Roman Protasevich on Thursday admitted in an interview he was plotting to topple President Lukashenko by organizing riots
Britain said on Friday an interview on Belarus state television with a journalist held after his plane was forced to land in Minsk was "disturbing" and that he was "clearly under duress."
Foreign Secretary Dominic Raab called for those involved in broadcasting the alleged confession by Roman Protasevich to be held responsible.
"Mr Protasevich's disturbing interview last night was clearly under duress & in detention," Raab said on Twitter, echoing condemnation by Germany and Belarusian opposition leader Svetlana Tikhanovskaya.
"The persecution of those defending human rights and media freedom in Belarus must stop," he said.
"Those involved in the filming, coercion and direction of the interview must be held accountable."
Protasevich was arrested on May 23 along with his girlfriend Sofia Sapega when their Ryanair flight from Athens to Vilnius was diverted and intercepted by a Belarusian fighter jet.
Protasevich is the co-founder and former editor of opposition Telegram channel Nexta, which galvanized demonstrations last year against Belarusian President Alexander Lukashenko's regime.
Looking uncomfortable in the 1.5-hour interview broadcast on Thursday, he said he had instigated the protests and praised Lukashenko, before breaking down in tears.
Tikhanovskaya on Friday dismissed the interview as the result of "torture," while German government spokesman Steffen Seibert called it "absolutely disgraceful and implausible."