MI5 thwarted a Chinese plot to attack Britain’s national security in the last week, its spy chief revealed today as he told of his frustration at the spy case collapse.

Sir Ken McCallum vowed today that he would ‘never back off from confronting threats to the UK’ after a critical espionage case collapsed when the Government refused to describe Beijing as Britain’s enemy.

After weeks of accusations that Sir Keir Starmer is ‘too weak’ on China, the spymaster urged the Government to ‘ensure that the UK is a hard target’ adding: ‘We need to up our game.’

In his annual threat speech, Sir Ken revealed that a major China spy plot had been disrupted in the last week alone as he warned of a 35 per cent increase in hostile state threat activity targeting Britain, with new plots and threats being detected ‘every day’.

In an unprecedented intervention, the Director General chose to break with the longstanding tradition that MI5 does not comment on individual cases as he described his frustration that parliamentary researcher Chris Cash, 30 and Chris Berry, 33, were not put on trial for allegedly passing secrets to Beijing.

‘Of course, I am frustrated when opportunities to prosecute national security threatening activity are not followed through for whatever reason,’ he said.

But Sir Ken pointed out: ‘In the particular case that I’m sure you have in your mind the activity was disrupted’ adding that his team had ‘every reason to feel proud of the detection and disruption job that they have done in this case’.

He said: ‘Clearly when we believe there has been activity threatening UK national security, convictions are great, we work very hard with our police colleagues to make them possible and so it’s frustrating when they don’t. I would invite everyone to just not to miss the fact that this was a strong disruption in the interests of the UK’s national security.’

Speaking at Thames House, Sir Ken vowed: ‘I am MI5, born and bred. I will never back off from confronting threats to the UK, wherever they come from.’

He said Britain needs to ‘defend itself resolutely against threats’, adding: ‘In this new era, with multiple overlapping threats on an unprecedented scale, we need to up our game.

‘We can’t rely solely on investigating and disruption. Together, we have to ensure that the UK is a hard target. 

‘We want our adversaries to think twice before acting against us.’

In pointed remarks, Sir Ken said there were ‘policy choices’ for Government which ‘lie in exactly which lines you draw, which balances you strike’.

He warned that MI5 was in a ‘new era’ of unprecedented threat saying: ‘In 2025, MI5 is contending with more volume and more variety of threat, from terrorists and state actors than I’ve ever seen.’

He also spoke of ‘rising aggression on UK soil’.

‘State threats are escalating. In the last year, we’ve seen a 35 per cent increase in the number of individuals we’re investigating for involvement in state threat activity,’ he said.

‘That means espionage, including against our Parliament, our universities, our critical infrastructure.

‘But now, states are also consistently descending into ugly methods MI5 is more used to seeing in our terrorism casework.

‘My teams are routinely uncovering attempts by state actors to commission surveillance, sabotage, arson, or physical violence, right here in the UK.

‘We are dealing with these threats every day.’ 

MI5 has tracked more than 20 potentially lethal Iran backed plots in the last year.

Sir Ken described how MI5 is battling ‘near record volumes’ of terrorism investigations adding: ‘In 2025, a more hostile world is forcing the biggest shifts in MI5’s mission since 9/11.’

MI5 has disrupted 19 late-stage terror plots since 2020 and has intervened in ‘hundreds of developing threats’.

The spy chief warned Al Qaeda and Islamic State are becoming ‘more ambitious’ seeking to recruit youngsters in the ‘squalid corners of the internet where poisonous ideologies’ lurk.

When asked directly whether China posed a national security threat, Sir Ken said: ‘Do Chinese state actors present a UK national security threat?

‘And the answer is, of course, yes they do, every day.’

But he defended the Government’s deputy national security adviser Matt Collins who refused to say China was a national security threat leading to the espionage case against Mr Cash and Mr Berry to collapse in September.

Sir Ken described Mr Collins as a ‘man of high integrity and a professional of considerable quality’.

The MI5 chief would not be drawn on the number of people involved in Beijing’s operations to target Britain, telling reporters: ‘Try not to think too much just in terms of classic, card-carrying spies based out of embassies in the Le Carre mould.’

There were a ‘whole host of ways in which Chinese state actors are able to collect information of value to them’, he said.