British Prime Minister Rishi Sunak said he had raised his concern over any Chinese interference in Britain’s parliamentary democracy during a meeting with Chinese Premier Li Qiang at a G20 summit in India, after the reported arrestof two alleged spies.

The Sunday Times reported that one of the people arrested on suspicion of spying for China was a researcher in the British parliament.

Sunak said he was limited in what he could say about an ongoing investigation but told reporters he had raised “his very strong concerns about any interference in our parliamentary democracy, which is obviously unacceptable”, with Premier Li.

Sunak’s Conservative government has sought a thaw in relations with China, engaging with Beijing on matters such as climate change but also criticising it in several areas including human rights.

Sunak said he raised areas where there are disagreements, but the meeting showed the value of the strategy of engaging “where it makes sense”.

“I think the right thing to do was take the opportunity to engage, to raise concerns specifically, rather than just shouting from the sidelines,” he said.

A Chinese readout from the meeting did not mention the spying allegation but welcomed Britain’s expanded practical cooperation with China, adding Li had said that “the two sides should properly handle their differences”.