"I'm so sorry," apologises Paul Wedgewood, CEO of Splash Damage and game director of Brink. "I've just realised that they inverted my controller when they were playing between presentations. I'm one of those old-school inverted guys and I absolutely can't play the other way round. Next time my team work on an interface for E3 I'm going to make sure there's an invert button right there on the screen that I can use!"

A throwaway moment during the behind-closed doors live gameplay demo of the game publisher Bethesda had considerably talked-up pre-E3. But it provides interesting insight into the mindset of London developer Splash Damage, responsible for the Enemy Territory series for id Software, and what it's trying to do with the hugely ambitious Brink. The game marks the studio's transition from a hardcore PC FPS dev into a multiplatform FPS dev. Wedgewood's "old-school inverted" preference shows that, despite the fact that Brink will no doubt make a huge splash on Xbox 360 and PS3, underneath it all PC FPS principles keep the engine running.

Going in to this presentation, we're not sure what to expect. Leaving it, we're convinced that Brink could well be one of the best shooters of 2010, and a candidate for our game of E309. It's not the stylised art design, an interesting fusion of Mirror's Edge-esque near future pristine whites and blues and Fallout 3-style shanty-town browns and greys that has us enthused. Nor is it the Smooth Movement Across Random Terrain (SMART) system, which allows players to vault and climb and slide over entities simply by holding down a button and aiming the targeting reticule up or down. What's best about Brink, what could make it a boundary pusher, a game to change the FPS genre forever, is how it blurs the lines between offline and online play so convincingly that it's hard to work out the difference between the AI and real players.

Brink takes place on the Ark, an immense, artificial floating sea city built as part of a contemporary green vision. Now, in 2035, the reported rise in the Earth's oceans has made the Ark the last refuge for humanity, but it is buckling under the pressure of an isolated and horrific civil war. It is to this backdrop that players pick between one of two factions (the Resistance and the Security), and allows Splash Damage to take them to the brink.

The Airport is a pristine, deserted district.

Wedgewood begins the demo in one of the Ark's districts, the Airport. Deserted for 20 years, the Airport is free from enemies and is a pristine, shiny place that DICE might have crafted for Faith to play with. "What I want to talk to you about first is kinesthetics," Wedgewood says, "and what we're doing to try and improve, just in general, how it feels to play a first-person shooter."

Players can walk around, spring and jump just as they can in any FPS, but SMART removes "frustrating artificial constraints". By holding down the SMART button and aiming the targeting reticule up, for example, the game will automatically vault the player over geometry, a set of chairs for example, allowing incredibly agile movement not just horizontally, but vertically. It works for sliding, too. Wedgewood walks through a set of red beams, setting off an alarm. He tries again, this time holding down the SMART button and aiming down. He automatically slides under the beams without losing momentum. SMART makes Brink less like the complex Mirror's Edge, which it at first suggests, and more like the momentum-based Prototype.

The upshot of all of this is that it allows Splash Damage to create much more complex geometry because it no longer has to place entities that tell the player where they can vault, mount and slide. "I'm a fairly chubby guy," explains Wedgewood, "but I reckon even I could get over a five foot wall. Isn't it frustrating when you run up to one in a shooter and you can't because the designer decided you're not supposed to mantle that point? This frees our designers to design whatever the hell they like and make it much more like the real world. This is not a system simply for newbies. The idea behind this is to improve the way you play the game."

SMART, however, is not Brink's most impressive feature, and it is not until Wedgewood takes us into Container City, another of the Ark's districts, that we see it for ourselves. The area was originally a dockyard where the Ark's wealthy inhabitants stored their prized possessions. The fully robotised system enabled them to literally phone room service and order up their goods. However, around 20 years before the events of the civil war the Ark lost contact with the rest of the world. The result was a massive influx of refugees that turned Container City into a sprawling shanty town.

SMART makes the environment your plaything

Playing as a heavily customised (there are 19.2 billion different character creation combinations and variations) member of the Security, seen as oppressors by the residents, Wedgewood's mission is to escort a bomb defusal robot and to try and track down the location of a dirty bomb. A team of muscle-bound hard nuts is stood at the entrance to the city. The stunning-looking sea behind them ripples under the sun. Sleek, futuristic towers can be seen protruding from the water in the distance. Seagulls spiral overhead, singing their song. The grinding of metal containers is heard from within the rusting innards of the city, a place that rekindles memories of Fallout 3's stunning Megaton. The team discuss the mission ahead. It is to be a quick, clean and quiet escort. Enemy fire puts paid to that, and all hell breaks loose.

Immediately we see what Wedgewood meant when he talked about blurring the lines between offline and online play. In Brink you play the same in-game character irrespective of whether you're playing offline or online. As you advance your, created character is moulded with graphic alterations, but also with gameplay-affecting abilities. Different body types affect play style. You might have a huge character, basically a meat shield, which as a result of his size has less freedom of movement. Conversely, a skinny guy will be fast and able to jump further. Abilities you unlock for each of the combat roles allows you to further specialise with weapon unlocks and upgrades.

In-game, via Command Posts that are captured during play, you're able to dynamically change your class and load-out on the fly. The Soldier, for example, is for players who like pulling off cool mid-air headshots and blowing stuff up. The Engineer can deploy defensive turrets and plant mines. The Operative is the stealth class, excelling in getting behind enemy lines and up to mischief. What's different is how the game is affected by your class changes and objective choices. Wedgewood starts as an Operative with the Assault load-out, which gives him a light submachine gun. If he had chosen to start as a Soldier, it would be his job to destroy a closed gate that's blocking the bot's path. As the Operative, however, the game automatically generates a number of missions that he's able to pick from a radial menu, each one granting a predetermined number of experience points (like in CoD4, XP pops up above killed enemies). He picks "Interrogate the Enemy". A sat nav arrow appears at the top of the screen, directing him to a down, but not out, enemy. He approaches the crawling bad guy. An iPhone-like device appears in his left hand and two crab-like claws protrude from the forward corners. It's a taser of a sort that zaps the target. After a few seconds of pain he squeals, "damn you, I'll talk!". The mission is completed, your squad commander radios in to tell you new information has been received. It's a comical moment, really. One) once the guy talks you celebrate with a thumbs up, and two) he doesn't actually say anything other than he'll talk, which, we suspect, isn't exactly the most revealing of statements.

Still, completing this objective has bought the Security a little more time, and has revealed new objectives that Wedgewood's team can pick from. He looks for something else to do. Via the radial menu he picks the mission that'll give him a whopping 500XP - "Repair the Crane" - but it requires a switch to the Engineer class. The sat nav directs him to a Command Post that's just been captured. He switches, picking the Close Combat load-out (shotgun fun and turret placement for long-range support). Once switched, the Squad Commander acknowledges the change. The team is alerted to the mission he's on, and new missions are automatically generated for Wedgewood's co-op friends: two Splash Damage team members button-mashing behind a wall. Wedgewood mentions it like it's only a trifle feature, but it is incredibly exciting: Brink will support eight-player co-op drop-in and out play. He repairs the crane, it picks up the bot and carries it further forward, pushing the front line and the enemy back.

The only limit to your movement is the sea that surrounds the Ark

He switches to the Soldier, selecting the Heavy load-out that grants the heavy explosive charge and the grenade launcher. He picks a mission to destroy an obstacle that is blocking a shortcut for the bot. He plants explosives, running and gunning up pipes and ledges, SMART facilitating the kind of agile movement rarely seen in an FPS. Boom - the bot reaches its objective and a cutscene plays out. The team cut open a canister - something mysterious and fantastic is inside. "Control - what did you say our objective was?" The demo ends.

It's been a thrilling presentation, one that's sent the hairs on the back of our necks reaching for the sky. While Wedgewood promises that the game will be fully playable single-player, as either a member of the Resistance or the Security, with all the narrative-driven action you'd expect from a single-player triple-A FPS, it's the multiplayer side of things that genuinely excites. Eight-player co-op, dynamically changing objectives, class-based gameplay, CoD4-style progression... it's like Killzone 2's multiplayer spliced with an MMO. Then he mentions something that gets us even more excited. All the action demoed will be playable competitively with persistent characters. So, eight versus eight, dynamically changing missions and class changing. Wicked.

In many ways Brink is the natural evolution of Splash Damage's online PC-focused Enemy Territory series, but as far as console shooters go it's practically revolutionary. 360 and PS3 owners schooled on the online offerings of CoD4 and Killzone 2 should be very, very excited. And, to be honest, so should everyone else.

Brink is due out for Xbox 360, PS3 and PC in spring 2010.