In 1997 Zoe Broughton worked undercover inside HLS as part of a Chanel Four series, Countryside Undercover.
Her investigation showed workers punching beagle puppies in the face and home office inspectors failing to do their job.
Ever since I was young I used to wonder what went on behind the high barbed wire of the huge animal-testing laboratory down the road. I decided to apply for one of the lab's many vacancies advertised in the local paper, to see for myself.
A few days later I got an interview for a job as an animal technician. The pay was about £120 for a five-and-a-half-day week. I made myself sound keen and stressed that I had experience of working with animals.
They checked my name to see if it appeared on any animal campaign lists and before I'd come to terms with what I was about to involve myself in I was working in one of Britain's largest animal testing laboratories.
I don't know what to expect, not even which department I will get sent to or how I will respond to seeing animals in pain. To fit in, I make up a false past. I can hardly reveal I am a filmmaker. But I am worried that I may something that might blow my cover. I am assigned to the dog toxicology unit.
I've always had pet dogs, but as we enter the building the noise and smell hits me. I cannot stop my face showing the shock. I notice immediately that the little puppies are keen to play, whereas the older dogs are wary of human touch. Some stay at the back of their cages and don't even move when I give them their food.
My job is to look after a room of 32 puppies. On the first afternoon I am asked to check the health of my dogs. I am shown how to do it, but trying to check teeth and paws on a wriggling little puppy seems almost impossible. Later I read the Home Office guidelines and it states that it has to be done by a competent person. How can I be competent on my first day at work?
All the dogs had their own distinctive characters and I was shocked to find out that they would al be put down. By the end of the day I was mentally and physically exhausted.
The hardest job is putting the young puppies away after their one hour of exercise in the small concrete corridor between the two rows of cages. They paw at me with their shitty feet; I pick one up, read the number tattooed in its ear and walk the length of the room to find its cage; all the while trying not to tread on paws and slip in the fresh shit. It's repulsive and by the end of the each day my lab clothes have turned from white to brown.
I have to help take blood samples. They call it "doing a bleed". I bring the first dog out and sit her on a chair beside me, holding both front paws in one hand and holding the chin up with the other. The animal technician shaves the dog's neck and then plunges the needle in. She continues bleeding afterwards.
I get blood on my arm and I see the other dogs look and know what is coming. Some grip the floor cringing and a couple try to dart past me and escape. Often the technicians can't find a vein. I count one needle being put in three times and once under the skin prod in different directions 15 times before finding a vein. I feel pretty queasy.
I am told not to use so much sawdust as "one shovelful is enough and it needn't be piled up." There is no bedding and this is all the dogs have on the concrete floors. The Home Office inspectors turn up. I don't see them look in any of the units I deal with - they just stand outside the dog rooms and chat with the technicians.
Another visit from the Home Office inspectors. This time I see them outside in the corridor a technician tells me to sweep the floor I sweep it, but they don't enter my side of the laboratory. I've now seen them arrive twice, but I haven't seen them look at a dog yet.
I still feel physically sick with nerves. The Independent Television Commission (ITC) has granted me permission to film what is going on. The camera equipment is strapped to my body. It is very bulky and I am worried because it is visible every time I bend over.
The worst day yet, as the experiments started on my 32 puppies. The test involves putting each dog in a sling and injecting a chemical used in scanning of human livers. Two are sick as they are being injected, some of their legs swell up and on top of this the puppies have 10 blood tests each through the day. The technicians keep saying that "these dogs are too young for this type of experiment as their veins are too small" - so why have they got them so young? If the puppies wriggle, they are hit or shaken by the scruff of their necks. I feel like a torturer. I hold them and soon get their blood on my hands.
I help prepare the doses for another experiment - it is an agrochemical toxicity test for a Japanese company. A lot of the tests in my department were testing for the toxicity of herbicides and fungicides. The man I am working with measures out the compound and I put it into capsules. He is meant to print out the weight of each dose on a computer so it can be checked. What he actually does is measure one dose correctly, print this out seven times and then make the next six doses for the week far more quickly and with less accuracy. This means the dogs are not getting the right dose: these experiments may be invalid.
Walk into my unit and one of my puppies, number 1619, has half a pint of congealed bloody faeces around his cage. The vet looks at him and says it is all right to continue with the daily doses.
I'm finding it hard to watch these needles being repeatedly put into the dogs legs, over and over. One technician gets so angry when he can't find a vein that he shouts and quickly jabs the needle in repeatedly, often going right through the vein. Twice I have seen him give up and squirt the rest of the liquid into the bin.
I have had plenty of opportunities to read the files. I have been writing notes on scraps of paper and have now established which experiments are in which rooms, who's sponsoring which companies, the compounds being tested and how each is being administered.
Today I film the pictures of the animal technicians' pets on the wall - many of them talk non-stop about their lovely pets and then go back to work.
We have now finished the experiment with my puppies and today we have to go through the whole blood-testing rigmarole again. I cannot believe the animal technicians' attitudes - they are messing around while trying to take blood. One technician pokes, tickles and fools around with the man he is working with. This makes the process of finding a vein take even longer.
They've started the post mortems on my dogs. Today I carry my favourite puppy along the corridor to what are known as the Death Row cages. I spent last weekend deciding whether to blow this whole project and smuggle her out - but I must think of the future of the other animals here and hope that my film will help all of them.
I have just walked out of the laboratory for the last time. I wanted to say goodbye and pet the dogs, but I've found it so hard loving those about to be put down that I kept my distance at the end. I don't think anybody suspects me. I have followed the whole process with my puppies, from the settling-in weeks, through experiments to the post-mortem. As I was leaving, they told me my chores for the next morning - nobody knew I would not be there, but in the edit suite, assembling the evidence of their cruelty."