It is “completely unforgivable” for a foreign power to engage in espionage in Parliament, the SNP’s Ian Blackford has said.

The party’s former Westminster leader, who previously sat on Parliament’s Intelligence and Security Committee, warned that the UK risked being “asleep at the wheel” when it came to the threats posed by China.

Over the weekend, the Sunday Times reported that a 28-year-old Edinburgh based parliamentary researcher and another man had been arrested on March 13 on suspicion of spying for Beijing.

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Officers from the Metropolitan Police’s Counter Terrorism Command, which oversees espionage-related offences, are investigating.

Both men were held on suspicion of offences under Section 1 of the Official Secrets Act 1911, which punishes offences that are said to be “prejudicial to the safety or interests of the state”.

They have been bailed until early October.

The researcher at the centre of the row had links with senior Tories including security minister Tom Tugendhat and Foreign Affairs Committee chairwoman Alicia Kearns.

Speaking to reporters in Rutherglen, Mr Blackford declined to be drawn on the specifics, given the ongoing police investigation.

However, he said the UK had “to be very alive to the threats that we face”.

He added: “I was on the ISC when we did the Russia report, a report of course that was suppressed by Boris Johnson for so long.

“We cannot be asleep at the wheel when it comes to the threats that we face, whether it's bad actors coming from Russia, whether it's coming from China or elsewhere, but we have a range of security intelligence agencies and we must make sure that we're always on our guard.

“We're living with the consequences of the war in Ukraine, the outrageous attack on the Ukrainian people, by the Putin regime.

“This is very real. And all these things are happening on our doorsteps.

“None of us must take the threats which are there lately. We must make sure that we respond in an appropriate manner.”

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Asked if he was worried the UK was asleep at the wheel, he replied: “When you look at the Russian regime, you look at the Chinese, they behave in a different manner than we would do in terms of what's acceptable, what's responsible.

“And at the end of the day, all of us and this is something that goes right across party have got that responsibility of keeping people safe in our streets. That's the single most important thing that must come out of this.

“Let's leave the individual circumstances behind what's happened here, but the idea that we can have someone engaging in espionage or any of our parliamentary estates is something which is completely unforgivable.”