The opening scene of 28 Days Later shows a bunch of animal rights activists breaking into a laboratory. At first the lab seems pretty ordinary. There are caged animals, there’s a weasely scientist and undoubtedly there are some lousy coffee-making facilities. But then we find out that a bunch of chimps are infected with ‘rage’.

As is customary for a bunch of sallow, undernourished Morrissey fans, they lose all sense of reason and decide to free the animals. But then rather than hug its liberator, a deranged chimp decides to leap on the person’s face. Somehow I doubt this fitted with the activists’ plan. They probably foresaw hugs of gratitude, a stroll down the High Street to weep at the inhumanity swinging in the windows of butcher’s shops and a special playing of Bona Drag. They never thought they’d be meat for the apes.

But how apt is it to have animal rights activists bringing about the end of the world? I mean, if it’s not the mink ravaging the countryside, it’s the apocalypse. These lettuce-eating, people-loathing humanoids will press the self-destruct button with their knuckleheaded do-goodery gone do-badery long before the jihadists and neo-conservatives get their shit together.

An unfortunate survivor of the disaster is Jim, a bicycle courier. He awakens in a deserted hospital, unaware that virtually everyone around him has been consumed by a horrible virus.

One puzzling aspect of Jim’s survival is that he’s left naked in a hospital room. Since when is that standard hospital procedure? When do they leave you stark bollock naked? But then I guess that’s socialised health care for you. There’s no money for the little extras like hospital gowns.

But I guess Jim’s nakedness is meant to symbolise his rebirth in this new world and his vulnerability in it. For a brief time he will be a helpless innocent – he’s going to have to relearn everything he knows.

Much has been made of the opening sequence where Jim walks around a deserted London, but as enjoyable and wonderful as it is, it’s not really that creepy. I’m sure most Londoners have roamed the streets early one Sunday and have seen how deserted the city can be. If you go to certain parts, you literally won’t see anyone. And so therefore the sequence doesn’t quite have the creepy novelty factor that it aims for – I’m sure Londoners staggering back from a night club early in the morning have seen the quiet and the mess that Jim encounters.

All that being said, it is wonderful to see London filmed with such skill and verve. Somehow 28 Days Later manages to take most of the clichés of filming in the Greatest City in the World (buses, parliament, Piccadilly Circus) and turn them on their head. We see a bus turned over on its side, parliament looks over a ghost town and Piccadilly Circus has become a home to missing persons flyers. It’s nice to see someone doing something different with the city.

One of the disappointing aspects of the London sequence is that it has to end. All too soon Jim stumbles upon a couple of survivors and the story kicks into gear. I think the film could have sustained a bit more of Jim’s loneliness. Thankfully, though, the film doesn’t collapse like I Am Legend when other people turn up.

That’s not to say that the script is anything special. In fact, in several instances, the film succeeds despite the script. This is especially true when Jim hooks up with the survivors. The exposition is pretty clunky.

However, even the acting can leave a lot to be desired at times. Cillian Murphy is excellent as Jim, and Brendan Gleeson is excellent as always, but the girl who plays Hannah is pretty awful. Her line delivery is consistently atrocious. I also think that Naomie Harris isn’t particularly great. She has the intensity that her role requires but she doesn’t necessarily have the acting chops – her performance doesn’t always feel particularly natural. Harris is obviously trying hard but she isn’t always succeeding.

Some of the soldiers, too, aren’t particularly great. There’s a dweeby private who seems to be touched in the head (the character is far too buffoonish – when he gets stabbed in the chest his eyes bulge out of his head like he’s a cartoon character) and there’s a cockney who is incredibly exaggerated – he’s like an EastEnders character on crack. Having said that, the cockney is so atrocious and so vile and so over the top that his death is incredibly satisfying – Jim literally buries his fingers in his head.

But while some of the acting and some of the writing disappoint, the direction is always a joy. The film has a very dirty, gritty feel to it. The digital cameras totally take the sheen off the picture. But at the same time the energy Boyle brings to the film ensures that it’s incredibly cinematic. The film feels a lot more expensive than it is.

The action set pieces also impress. They all have lots of tension and excitement. And this is made even more remarkable by some of the bad writing that brings them about. For instance, there’s a sequence where the characters get a flat tire in a tunnel. Before driving into the tunnel Jim says that it’s a shit idea for them to take this route, and he turns out to be right. But even though Alex Garland tries to write himself out of the situation by making Jim self-aware, it doesn’t stop the sequence from being highly contrived.

Another contrived sequence is when Jim wanders off from the group into an empty building. It’s a terribly hackneyed way of building a shock, but somehow, because Boyle is making the film, it still manages to work.

The final act of 28 Days Later has been criticised in some quarters. People who love the beginning see it as anti-climatic. But I think that the final third works pretty well. Sure some of the acting is lacking, but the banality of the soldiers’ evil seems correct – given the end of the world, they’re desperate for pussy. And it’s fun to have the infected run riot in the soldiers’ base and kill everyone. It kind of becomes a black comedy in the end.

However, as enjoyable as the final action set-piece is, you still have to put up with a huge flight of fancy. The bit I’m talking about is when Jim manages to climb over a wall with barbed wire on top of it with both of his hands bound. How the hell did he manage that? Somehow he becomes an Irish Superman.

But in the end Jim actually becomes more like the infected. He ends up killing people with his bare hands in a murderous rampage. As always in ‘zombie’ films, the zombies are the underclass – they’re loathed, they’re mocked and they’re figures of fun (the soldiers keep an infected person chained up and take pleasure in mocking him – it doesn’t seem to be a coincidence that he’s black). So in the end we’re almost asked to empathise with the infected. As violent and as base as they are, their actions are at least not premeditated. Their evil isn’t based on whims or prejudice. They’re slaves to their senseless bloodlust. Ordinary people on the other hand should know better. They should be rallying together. And so therefore the final triumph of Jim, Selena and Hannah is a victory for decency – the thing that will get us through hard times is belief in the family unit; no matter how hard things get we must always have the strength to think and feel.