For RSPCA Inspector Alan Barnes the day starts early. He's hardly out of his front door before he has a suffering creature thrust into his hands.

It's a fledgling blackbird, which moments earlier had been cheerfully presented to Alan's neighbour as a gift from his blood-thirsty cat.

Alan packs the bird snuggly into a box, and places it carefully in the back of his RSPCA van, before heading off to work.

Based in the charity's impressive St Philips headquarters, Alan is one of three full-time RSPCA inspectors covering the city.

They're at the cutting edge of the RSPCA's work – preventing cruelty to animals on a daily basis. Most of the "rescue work" is left to the animal rescue officers.

Inspectors like Alan spend their time knocking on doors, and investigating allegations of willful or negligent cruelty to domestic creatures.

We join him on an average day, to see Bristol through the eyes of an animal welfare inspector.

Suddenly the world can seem a cruel place when you spend all your time investigating these kinds of allegations. Last year, Alan brought four successful prosecutions against people who had mistreated their pets, but rescued hundreds of animals from miserable lives.

One of the prosecutions was the widely reported case of Andrew Wilson who was convicted in January of becoming the first person to be convicted of getting a dog drunk.

The 31-year-old chef, of Ringwood Crescent, Southmead, forced his five-year-old bull mastiff cross to drink cans of Stella Artois, before battering him with a broken chair leg.

Wilson was banned from keeping warm-blooded animals for a year. He was also sentenced to 150 hours of community service.

But Alan's most disturbing case dates back a couple of years.

"The one that really upset me was a collie dog that had been kept locked up in the kitchen of a Southmead house for five years.

"The poor dog was living in absolute squalor. There was five years of the dog's defecation built-up into a thick layer on the floor. The woman had not even been into the room in all this time – just occasionally throwing the dog some food.

"I called the police and we forced entry to rescue the dog, which was in a pitifully emaciated condition. It was heart-breaking.

"Thankfully the dog made a good recovery, and was rehomed. We prosecuted the owner. As I remember, she was fined and oddly enough was tagged and given a curfew.

"It can be frustrating, because when you've seen the animals in this kind of condition, the rulings of the courts always seem too lenient."

We arrive at the RSPCA clinic in St Philips, where a veterinary nurse takes a look at the young blackbird.

It was hardly injured – just a little bruised – and would be taken down to the RSPCA's bird facility, West Hatch, near Taunton.

"They'll look after it down there until it fledges," Alan explains. "After that it should fly off and live a normal life."

Glowing warmly from this first success story of the day, we drive across the city to visit the home of a man in Whitehall, who has made an unusual discovery in a nearby alleyway.

A ferret has been abandoned with its cage door open.

"People get these kinds of pets, then get fed up keeping them," Alan says, "so they abandon them. Sadly, we get plenty of these kinds of calls."

The pretty little ferret joins us in Alan's van for a lift back to the clinic, for a quick check-up, before joining the RSPCA's rehoming list.

Alan has worked as an RSPCA inspector for the past 10 years.

"I graduated from the University of the West of England with a degree in marketing," he explains as we drive along. "I didn't know what to do with myself, and I ended up trying my hand at all kinds of jobs – I've worked everywhere from construction sites to leisure centres. But one day I spotted this job advertised in the Evening Post, and I immediately thought – that's the job for me."

Since taking on the role, Alan has also undergone specialised training in rope work and abseiling – which means he can be called to assist with the rescue of animals trapped on cliffs or caught up in floods across the South West.

"People often say 'it must be lovely working with animals all day', but for me this job is much more about dealing with people," he says. "The animals are never a problem."

Alan was assaulted by a member of the public the previous week.

"I'd only got as far as knocking on the door, but when the man saw my RSPCA uniform, he lunged at me – nearly knocking me off my feet.

"I called the police, because it was clearly unacceptable. But actually, I've been lucky. That's the first assault I've suffered in 10 years of service."

Alan likes to think this is to do with his impressive people skills, but his sturdy frame probably helps – he towers over my decidedly average 6ft height.

After checking his diary, Alan sets off across the city once again. He wants to visit a property in Horfield, where neighbours reported seeing a pet collie with a bad flea infestation.

As if on cue, as we walk up to the property the owner walks down the path taking the dog for a walk.

The dog seems well loved, and Alan is reassured after taking a look at the prescription flea medication being administered to the animal.

"Nobody likes to see the RSPCA turn up on their doorstep," he says. "But most people are reasonable. They respect the authority that the uniform represents, and often the shock of having a visit from an RSPCA inspector can be enough to make them take action for their pet's welfare."

Alan puts this authority to good use on the very next call. We knock on the door of a Horfield man who had previously been convicted of animal cruelty, after leaving his two dogs in a hot car. Both dogs died of dehydration. The man was banned from keeping animals for 10 years.

"I've had a call from somebody who seems to think the man might have been seen recently with a puppy," Alan explains. "If I think there is evidence that he is breaching his ban, I'll get the police involved."

Although there's no sign of an animal at the property, Alan is not convinced that the man – who has learning difficulties – has not been involved with a puppy in recent weeks. He administers a "stern talking-to", by way of warning.

With Alan's day drawing to an end, there's one more call to make. It's to a house in Filton, where the residents have been reported as keeping a rabbit in a hutch in a brick outbuilding.

"The caller said there was no natural light in the building, and that the animal was in darkness 24 hours a day. I'd hate to think of any animal living in those kinds of conditions," Alan says.

We call at the property, and the owner unlocks the padlock on the brick-built shed. Sure enough, we find the rabbit in the darkness.

The creature is suffering some sort of eye infection – with puss under both eyes. The owner admits the rabbit has been in this state for some time. Alan offers him an ultimatum – either he agrees to take the animal to a vet within 48 hours, or he signs it over to Alan, so he can return it to the clinic. The man is more than happy to sign on the dotted line.

"It belongs to my 15-year-old boy," he says. "He got it when he was 10, and he's always looked after it. But he's getting older now, and has started finding other interests."

The bunny takes his place in the back of Alan's van, blinking in the daylight. But his future is uncertain.

"He is five years old, which is a good age for a rabbit," Alan says. "If the eye infection is serious, it might be that the RSPCA vet decides to put him out of his misery. I think that would still be a merciful escape from living in constant darkness.

"But if it's not a serious condition, our veterinary staff will treat it, then we'll try to rehome him.

"It's been a fairly routine day for me," he says. "But you go home each night feeling that you've done some good for a few animals out there. At the end of the day, that's a very good feeling."