The target raced into view, running full pelt from the alley. Was this the suspected armed robber we were searching for? ‘Police!’ I yelled. ‘Stop!’ He ignored me – but my eight-year-old German shepherd Finn now had him in his sights.

The suspect was a young man, slim and athletic, with his right arm hanging oddly, which I realised was because he was holding something – it looked suspiciously like a police baton. He was armed.

‘Police officer with a dog! Stop! Stop or I’ll send the dog!’ Again my warning was ignored. I let Finn go. As the man tried to scramble over a fence, Finn took hold of his lower leg in his mouth and pulled until the suspect was face-down on the grass.

The man then suddenly flipped on to his back. I took hold of Finn’s collar and told the suspect: ‘You need to listen to me. You need to stop fighting my dog.’

Once Finn was active, of 32 police dogs on our force he topped the league table for arrests in three out of seven years

Suddenly, something caught my eye. It was a massive piece of dark metal which he appeared to be pulling from Finn’s chest. It was covered in blood. It was a knife – as thick as a ruler. It was ridiculously huge, like a hunting knife – the blade alone must have been 10in long.

‘You’ve just stabbed my dog!’ I gasped. ‘You piece of s***!’ Now the man lunged forward towards me. I had no time to react, but Finn did. He tugged harder on the man’s leg, shaking it violently. All the suspect managed to do was slice open Finn’s head, and as my hand was close by, he sliced that open too.

Still Finn refused to let go, pulling on the man’s leg as I lifted the suspect before slamming him back on to the ground. I had to do it again before he finally dropped the knife.

When back-up arrived, I finally told Finn to let go. His belly fur was slick with blood. My first thought was to check him over. I lifted his leg and heard a blood-curdling noise – it was air being sucked into his body through a hole that shouldn’t be there. Blood was pouring out of him and going all over my hands and down my trousers. Was my brave boy lying there, dying before my eyes?

We would come to forge the closest of human-canine relationships. When my colleagues weren’t looking, I was down on the floor with my new mate, having my face licked, my ear chewed, my pockets raided and boots tugged, my arms clamped and munched on, my heart melting.

Finn and I had been partners at Hertfordshire Constabulary for seven years. During that time, he’d tracked more than 200 people: murderers and rapists, burglars and missing persons, car thieves and assault suspects.

He’d been just nine months old when I’d first picked him up from his foster family – by far the naughtiest puppy they had ever housed. In the time they’d had him he had destroyed eight pairs of slippers, one rug, one chair leg and one dog-training bite sleeve.

When I collected him one Friday in January 2010, it really did feel as if all my Christmases had come at once. I was a 32-year-old father-of-two, yet I felt like a kid in the proverbial sweet shop.

We would come to forge the closest of human-canine relationships. When my colleagues weren’t looking, I was down on the floor with my new mate, having my face licked, my ear chewed, my pockets raided and boots tugged, my arms clamped and munched on, my heart melting. It was everything I’d hoped for and more. Once Finn was active, of 32 police dogs on our force he topped the league table for arrests in three out of seven years. It was his phenomenal tracking that really marked him out as a superhero. He once picked up a scent that was two hours old and managed to follow it to find a woman with dementia who had wandered from her care home.

We had been doing a spot of training in the early hours of October 5, 2016, when the radios crackled into life, alerting us to an armed robbery in Stevenage.

A taxi driver had been robbed of his takings by a passenger. The driver had done the sensible thing – stopped the car, handed the money over, then run for his life.

In another incident, a second cabbie reported seeing another suspect with a possible weapon. First I checked out the location before going back to deploy Finn. At the sight of me running back to the van, he was already spinning in his cage in excitement to be released. He had studied my body language. I didn’t need to say a single word. I never did.

One minute he was hot on the tail of the fleeing suspect. The next he was lying in a pool of blood, dying before my eyes. I scooped Finn up in my arms and ran to my van.

One minute he was hot on the tail of the fleeing suspect. The next he was lying in a pool of blood, dying before my eyes. I scooped Finn up in my arms and ran to my van

Luckily the nearest 24-hour vet was only a couple of miles away. ‘Has he lost very much blood?’ one of the vets asked as I carried Finn inside. I sent them all back out to the van so they could see for themselves. Finn’s breaths were fast and shallow because, with his chest full of air, his lungs wouldn’t inflate. He was fading away.

It was like being at the epicentre of a violent storm: blood everywhere, matted fur flying, radios crackling, phones ringing, equipment beeping.

In the midst of it all, lying horribly still now, was my partner, being the good lad he had always been, trusting them and trusting me to take care of him.

Every time we moved him, more air whooshed into his chest. We were fighting a losing battle, despite the hand-operated chest drain the vets had now managed to put in. One of the few centres that had the facilities Finn urgently needed if he was to have any chance of surviving was based in Higham Gobion, a 20-minute drive away.

It was almost 4am when a police van arrived to take us there. Despite or because of the morphine, Finn became agitated, so to keep him calm I tickled his ear and whispered soothing things to him. The 20-minute drive felt like a lifetime, every passing minute of which I was expecting Finn to die. Once we arrived, the team set about immobilising him, ensuring he had sufficient oxygen and morphine, and trying to get a mechanical chest drain inside him. Ronan, the senior vet there, explained they would seal the wound and measure the air flow in and out.

There was good news: the injury was almost certainly confined to Finn’s lung. ‘But there’s nothing further you can do for him now, Dave,’ said Ronan. ‘Get your own injuries properly seen to, then go home and get some rest.’

Leaving my canine buddy behind almost broke my heart. ‘You can do this,’ I whispered, crying into Finn’s fur. He responded with a weak wag of his tail.

‘Please save my boy,’ I pleaded with Ronan. ‘He saved my life.’

Another officer took me to hospital. I was numb, exhausted and terrified. The vision of the knife, that flash of metal as it slid out of Finn’s chest. Then another flash as the suspect lunged a second time, aiming for my upper body, and Finn moving to protect me and blocking the weapon with his head.

By the time I was heading to hospital, my wife Gemma was on her way there too with our daughters. Gemma, who is also a police officer, had been told by her own sergeant that I’d suffered a minor injury, but because the girls were in the car and the sergeant has been on loudspeaker, she’d asked him not to tell her any more. At hospital, I told her about Finn’s condition and, of course, she burst into tears too.

Another officer took me to hospital. I was numb, exhausted and terrified. The vision of the knife, that flash of metal as it slid out of Finn’s chest

Rob Adams, a specialist soft-tissue surgeon, took over Finn’s care. Finn had suffered a punctured lung and needed emergency surgery. There was no guarantee he would survive. It was past three in the afternoon when we got the news Finn was out of surgery. ‘He really is the luckiest unlucky dog in the world,’ Rob told us. ‘He’s still with us, and the surgery’s gone well.’ Miraculously, the 10in blade had missed his heart.

When I was finally allowed to see him I was shocked. Finn was linked up to all sorts of machines and breathing aids, and all I could see was my big, brave boy so horribly diminished. Almost his whole body was shaved, beneath a blue protective jacket that kept all the tubes in place and protected his enormous surgical wounds.

AS news of Finn’s injuries spread, there were messages of support from all over the world. To see the good wishes and concern pouring in for my beloved dog over social media was astounding. If Finn’s life could be saved by love alone, he had it nailed. When I next saw Finn, he meandered rather drunkenly over the grass, appearing not even to notice me at first. But then I called to him and he started squeaking and wagging his tail just as hard as his body would let him. He buried his head between my knees, so I could massage his ears for him. It’s impossible to overstate how good that felt.

Finn continued to make amazing progress. If there weren’t any complications, he might be well enough to return to work after Christmas.

A couple of days after Finn came home, I posted on social media a pretty graphic picture of him sleeping by the fireplace, showing his torso almost fully shaved and his scar. Little did I realise the impact it would have. It was shared around the world and would go on to become the image that launched a campaign – one for what would eventually be called Finn’s Law.

The law around service animals is straightforward. The Animal Welfare Act covers cases of animal cruelty, but people who harm service animals are almost never charged under this legislation because the penalties are so insignificant and the law so ineffective.

The best that can be achieved if a police dog or horse is attacked and/or wilfully injured in the line of duty is to charge the suspect with having committed criminal damage. In terms of law they are considered to be of no more consequence than a piece of inanimate property.

Finn tracked him down to a stable and found the suspect hiding under a horse blanket. It was like he’d never been away, though his career was now drawing to a close

The interest in Finn grew. A short video, pointing out what a bizarre thing it was to compare an attacked service animal to a smashed window, saw an electrifying response – more than two million views in a matter of days. Once an online petition has 100,000 signatures, the Government is obliged to debate it in Parliament. Within days, the number of signatures for Finn’s Law hit 130,000.

On November 14, 2016, just five weeks after the attack, MPs debated Finn’s Law and a principle was agreed: the current law wasn’t adequate and needed to be reviewed.

Just over a month later, on December 20, Finn returned to duty. Almost immediately he was called into action when, after a stolen car had crashed into a Range Rover, the suspect had fled.

Finn tracked him down to a stable and found the suspect hiding under a horse blanket. It was like he’d never been away, though his career was now drawing to a close.

Finn’s retirement came at the end of March last year, something that had been planned long before the attack. It was never going to be easy to deal with. You work so closely with a dog that it’s like losing part of yourself. With Finn, given what we’d been through, I knew it would be even harder.

The young man who attacked Finn was found guilty but was sentenced to only four months. I felt let down because he received no penalty whatsoever for what he did to Finn. He received a separate sentence for every other offence – the assault on me and possession of the knife and also a gas-powered pellet gun. But for what he did to Finn – nothing. How could that be?

At the time of writing there has at least been progress in the form of a tweak to the sentencing guidelines for the Animal Welfare Act. But though this is obviously a step in the right direction, in practice it changes little.

We’re a nation of animal-lovers. We can and should do more. I really hope we don’t have to wait for another attack on one of these courageous animals before something happens. Before we finally have Finn’s Law.

:: Fabulous Finn: The Brave Police Dog Who Was Stabbed And Came Back From The Brink, by Dave Wardell with Lynne Barrett-Lee, is published by Quercus on February 8 at £16.99. Offer price £13.59 (20 per cent discount) until February 4. Pre-order at mailshop.co.uk/books or call 0844 571 0640 – p&p is free on orders over £15.