Keir Starmer has twice declined to directly condemn the jailing of dozens of Hong Kong’s most prominent pro-democracy figures, less than 24 hours after meeting China’s president at the G20 summit.

The UK prime minister was asked both during a BBC interview and at his press conference in Rio de Janeiro to respond to the jailing of the activists, including being asked if he would condemn the sentences directly, but he reiterated the importance of building bridges with China for the sake of economic growth.

Starmer said that UK “mustn’t lose … the opportunity for our economy”.

He was condemned by the former Conservative leader Iain Duncan Smith, who is subject to sanctions by Beijing, who said Starmer was “so desperate for trade they will turn a blind eye to all future atrocities”.

Those jailed are among 47 people, known as the Hong Kong 47, who were charged in 2021 under the national security law. Starmer raised the issue of the jailed media tycoon and pro-democracy activist Jimmy Lai with Xi Jinping at their meeting on Monday, as well as the sanctions imposed on parliamentarians.

Asked if he could condemn the sentences or needed to bite his tongue to prioritise the economic partnership, Starmer said: “Well, we want that close economic partnership, and China is the second biggest economy in the world, and therefore, I see that as an area where we can cooperate.

“But I do also think it’s right that when we have differences, we have a discussion about them, as we did yesterday in relation to Hong Kong. So I do think both of those things need to happen.

“What we mustn’t lose is the opportunity for our economy for a better partnership when it comes to cooperate on economic and trade affairs. But as I say, that doesn’t mean we don’t have those differences and it doesn’t mean we shouldn’t be frank about those differences, and that’s the approach that I took yesterday and will continue to take.”

Starmer also said in his opening address that he would always keep communications open with China, saying: “The lesson of history is the more we are able to deal with problems, the world is safer when leaders talk.”

The Labour leader had earlier been asked to comment on the prison sentences in an interview with the BBC but declined to do so. He said: “I’m driven by the fact that economic growth, getting our economy working properly so people feel better off, is the number-one mission of this government and that’s why a pragmatic, serious relationship is the right relationship to have with China.”

Duncan Smith said Starmer’s comments on Lai’s imprisonment had only mentioned his medical condition, rather than the charges against him. “It is clear Starmer, in refusing to condemn the sentences handed down … and not calling for Jimmy Lai’s release, means that he and his government are so desperate for trade they will turn a blind eye to all future atrocities,” he said.

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“It now appears we are returning to the failed ‘golden era’ project [of the David Cameron era] but this time on our knees. A once great country sells its soul for a dubious mess of pottage – what a shameful place to be as all those who looked to us for help will see how we are abandoning them.”

Opening his press conference on the final day of the summit, which included a significant weakening on the leaders’ position on Ukraine in the final communique, Starmer issued a veiled response to his critics on the number of days he had spent abroad during his premiership.

He said that his international obligations were solely for the benefit of British security and for the economy, saying the Labour government was “reviving the international influence that was neglected for years, rebuilding partnerships and using them to deliver on the things that matter at home”.

Starmer said: “Under my leadership, Britain will never be absent from the world stage.”