I'd never attempted to carry out an arrest before, but that changed yesterday (30 March) when I confronted Saudi General Ahmad Al-Asiri. "I'm placing you under citizen's arrest for war crimes in Yemen." Those were exact my words before a burly security guard pushed me out of the way and others held me back.

The general didn't take it very well. While firmly protected by a gaggle of bodyguards he turned round, looked me in the eye and stuck his middle finger up; a gesture that in the last 24 hours has become a meme shared by pro-Saudi trolls all over social media.

Since then I've had people commend me for my actions, but others have asked why I did it. After all, they say, he was here in a private capacity to address the European Council on Foreign Relations, a respected think-tank. What's so wrong about that?

Al-Asiri the war criminal

The first thing to say is that the regime Al-Asiri represents is one of the most authoritarian in the world. He is a senior adviser and spokesperson for a government that routinely carries out executions, has been widely accused of torture and would never allow the kind of protest I took part in.

He is not just a representative of the regime, he is also the frontman for the Saudi military and their terrible bombardment of Yemen. The bombing has lasted for over two years now, destroying vital infrastructure and killing thousands of civilians.

The evidence that Saudi Arabian forces have flouted international humanitarian law (IHL) in Yemen is overwhelming. Last year, a leaked UN expert panel report into the war reported widespread and systematic attacks on civilian targets, as well as starvation being used as a weapon of war. The punishment has been indiscriminate. One month after the UN report, Al-Asiri told Reuters, "Now our rules of engagement are: you are close to the border, you are killed."

Saudi forces haven't just shown a total disregard for international law and human rights, but also for the truth. In November 2016 Al-Asiri told ITV that Saudi forces had not been using cluster bombs in Yemen, only for the UK parliament to later admit that they had.

UK complicity in Saudi crimes

The UK's complicity in the destruction has been so absolute that it only made me more determined to stop the general. How could I ignore him when the government of the country I live in has offered political and military support for the appalling war that he and his colleagues have waged?

In fact, it's not just been supportive – it's played an utterly central role. Data compiled by Campaign Against Arms Trade shows that the UK has licensed over £3bn worth of arms to the Saudi regime since the bombing began, including the fighter jets flying over Yemen and the bombs falling from the sky. As I write this, UK ministers and civil servants are actively working to secure even more fighter jet sales.

The impact of the bombing has been devastating. There are already 17 million people in Yemen that are food insecure and need humanitarian intervention – how much worse does it have to get before the UK finally does the right thing and stops fuelling their suffering?

16 February 2017: A man examines the damage caused by an air raid that hit a funeral reception in Yemen's Arhab district Mohammed Huwais/AFP

We can't stay silent

I wasn't alone when I stopped Al-Asiri, I was joined by other peace campaigners, including very brave Bahrainis who have first-hand experience of what it means to challenge human rights abusers. Some of them have been beaten and tortured for protesting peacefully against the Bahraini Royal Family. They were victims of a violent crackdown that Saudi forces have supported every step of the way.

By the time I got home I had hundreds of Twitter notifications. Some were accusing me of physically assaulting Al-Asiri or of being an Iranian spy. I'd heard all about fake news, but I'd never been a victim of it.

Needless to say, neither of these things are true. I was peaceful every step of the way. Unlike Al-Asiri I believe that human rights are universal, and I had no desire to attack him or to physically hurt him. And make no mistake about it, had he been a spokesperson for the autocratic Iranian regime then I would have been just as quick to act.

It's a sign of how broken our political system is when a man like Al-Asiri, a senior adviser to one of the most brutal and oppressive regimes in the world, can be welcomed into Whitehall and invited to meet with MPs and whitewash his crimes to leading think-tanks. If real justice is to be done, then governments like the UK's need to finally stop putting arms sales ahead of human rights while people like Al-Asiri are arrested and investigated for war crimes.

I am only one person, and I did what I could to imbalance the injustice, but it's not my voice that needs to be heard. The ones that those in power really need to listen to are those of the millions of Yemeni people who are the victim of a humanitarian catastrophe – not those that are inflicting it.

Sam Walton is a peace campaigner, Quaker and anti-arms trade activist.