No single word describes the challenge that China poses for UK foreign policy. There is threat and opportunity; a requirement to engage and an imperative to be guarded. The Communist party in Beijing represses dissent and pursues its interests overseas with coercive nationalist determination. It is not a regime with which Britain can build a relationship based on common values.

But China is also a superpower with near-monopoly control of some mineral resources and pre-eminence in important manufacturing supply chains. Trusting friendship is not an option; hostile rejection is unrealistic. It is not easy to manage relations through private diplomacy, let alone under public scrutiny. But Sir Keir Starmer’s government has looked especially awkward in its response to the collapse of a high-profile espionage case, involving the alleged transmission of secrets from inside parliament to Chinese officials.

The Crown Prosecution Service dropped the case against two men, a parliamentary researcher and a teacher working in China. Both deny wrongdoing. The CPS says a conviction could not be secured if China was not named in government witness statements as a threat to national security – ostensibly a requirement of the Official Secrets Act.

Opposition parties have cried foul. There are ample policy papers and ministerial statements going back many years attesting to the threat China poses. The suspicion has been raised that political pressure was applied to drop the case through fear of offending Beijing and spoiling economic relations.

Ministers reject that claim and accuse the Conservatives of failing to fix flaws in the Official Secrets Act when they were in power. In parliament on Wednesday, Kemi Badenoch said the whole affair “stinks of a cover-up”. The prime minister responded that the Tory leader was “slinging mud”. He committed to publish witness statements that, he says, support the government’s account of events.

Something is clearly amiss if the CPS thought there was an espionage case to answer, but couldn’t bring it to trial. In a climate of endemic mistrust in politics, it would be prudent of Mrs Badenoch to beware leaping from scepticism to conspiracy theory. By the same token, if wider diplomatic and commercial anxieties really are unconnected to the case, the government should have been more transparent, earlier.

Partisan rhetoric has heated the debate without shedding much light on the underlying issue. There is more consensus on this question than the tone of party-political exchanges in recent days suggests.

In office, Conservative ministers, including Mrs Badenoch, picked their words carefully when describing the risks of overexposure to Chinese espionage and dependence on Chinese technology, often to the frustration of hawkish backbenchers. The suppression of political freedoms in Hong Kong was not opposed as robustly as pro-democracy activists there deserved.

Managing relations with an assertive superpower is complex. Judicious language does not necessarily indicate naivety about the danger. But diplomatic protocol should not prevent candour about the limits to engagement with a regime that is often hostile to fundamental British interests.

The current Labour government is not the first to send mixed signals on this point. If Sir Keir has a clear sense of how to strike the balance between trade with China and national security interests, ending confusion over the failed espionage case would be a good way to spell it out.

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