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Jenson Button

The man in pole position is Button as he tops the standings, 14 points clear of Barrichello and 16 ahead of Vettel.

He has , but even if Button suffers a mechanical problem or crashes out and the other two go on to collect points, then the Englishman would still lead going into the final race of the championship in Abu Dhabi; so he has that safety net.

Even so, you just sense that the 29-year-old would prefer to wrap this title up as soon as possible and if the weathermen could guarantee dry conditions on race day then I believe Button would clinch the championship this weekend.

But the forecast is so unpredictable with rain expected to disrupt some, if not all, of the sessions. And that throws far more variables into the equation.

A strong qualifying performance will be key to Button's chances. We've seen this season that when he qualifies out of position it's a bit of a scramble for him, and he certainly won't want to find himself having to overtake to get in the points here.

Button is facing criticism that he is stuttering towards the championship and instead should be trying to win the title in style, but he is not a man for the grand gesture.

The Englishman has modelled himself on four-time champion Alain Prost. He shares the Frenchman's smooth driving style and steady accumulation of points rather than charging his way to the championship.

Button has led the championship and he has maintained that advantage. He's stayed unflustered as his rival teams have caught up and the competition has intensified.

There would be a certain symmetry if Button claimed the title at Interlagos, as it was here than he won his first points in F1 for Williams nine years ago.

I was there on the day that Button was chosen to partner Ralf Schumacher in 2000 and I've watched him grow and mature since then.

In 2004, he took the fight to Michael Schumacher as BAR-Honda hit form and went on to claim his first victory two years later. He has continued to learn and mature through Honda's lean years, when it seemed that his career in F1 was petering out, and again through a winter of uncertainty when Honda pulled out of the sport last December.

If Button is crowned Britain's 10th world champion he will join a list of great and good drivers. Jim Clarke, Jackie Stewart, Lewis Hamilton are some of the greats while Button would arguably join Damon Hill and John Surtees among the very good.

That is not to say that the 29-year-old would be no less deserving of the title. His performance at the first part of the year was outstanding and he has taken the chequered flag in six races this season, which is more than Hamilton won in his championship-winning campaign.

Button is a worker and if he is crowned the 2009 world champion it would be a reward for talent, patience and determination.

Rubens Barrichello attended a photo shoot at a local football club in his native Sao Paulo ahead of the Brazilian GP

Rubens Barrichello

Barrichello is Button's closest title rival and he needs to out-score his team-mate by five points to keep his chances alive.

The Brazilian probably can't believe his luck; 12 months ago he was driving in a car that was going nowhere for a Honda team with no future, now he is in with a shout of the world championship as the oldest man on the grid. What a turnaround!

The 37-year-old grew up within earshot of Interlagos and cut his teeth on the karting track along the back straight but just as Button hasn't had great success at Silverstone so Barrichello hasn't been blessed at Interlagos.

He has finished here just five times in 16 years and his best result is third for Ferrari in 2004.

If the race is dry on Sunday then I would favour Barrichello to finish ahead of Button, but I would still pick the Briton to claim enough points to take the title. If it's wet then anything could happen.

The bottom line is Barrichello needs the race of his life at Interlagos and for luck to shine on him for once on home soil.

Brawn team principal Ross Brawn says it will be a fair and open fight between his two drivers. He wants them to race each other and if the team loses the title as a result then so be it.

Ross Brawn is a big fan of Barrichello. He knows his technical input is important to the team and that the Brazilian found himself muzzled as Michael Schumacher's team-mate at Ferrari when he had the ability to win on a number of occasions.

But I wonder how much support Barrichello will have here this weekend. He was the first Brazilian driver to come along after the late, great champion Ayrton Senna and so much was expected of him.

Despite his success in junior formulae, it just didn't happen for Barrichello. He didn't see off Eddie Irvine at Jordan, he battled away at Stewart and was seen as little more than Schumacher's lap-dog at Ferrari.

I don't think the support for him will be as passionate as it was for last year's runner-up Felipe Massa.

If Barrichello is crowned world champion he would be a popular winner - he's always cheerful and a thoughtful talker - but I don't think he would be mentioned in the same breath as Brazil's previous champions Emerson Fittipaldi, Nelson Piquet and Senna.

Sebastian Vettel ponders his title chances ahead of the Brazilian Grand Prix at Interlagos

Sebastian Vettel

It is so simple for Vettel - he really has to win in Brazil.

After five non-finishes this season it looked as though the German was long gone but Singapore, where he finished fourth, was a big leg-up for him and his victory in Japan was outstanding.

He has nothing to lose and everything to gain.

In the final two races of the season, the Red Bull driver has to come first or second to have a chance of overhauling Button and he has to rely on the Brawns experiencing problems, too.

He has got to believe that he can emulate Kimi Raikkonen's achievement of two years ago, when the Finn came back from a 17-point deficit to clinch the title.

It is a major ask but if anyone can do it you would have to say it as him.

Vettel is the only man on the grid to have qualified inside the top 10 at every race this year and he was very impressive at Interlagos last year when he finished fourth in his Toro Rosso.

The German's chances in Brazil will improve markedly if it is a wet race. He has already proved what a master of the wet he is, with rainy wins in China this year and at the 2008 Italian GP.

His car also comes into its own in the wet and my information is that the Red Bulls could be a real handful for the Brawns if it does rain here.

There are one or two errors that Vettel needs to iron out but the 22-year-old is most definitely a champion in waiting. If he doesn't pull it off this year against all the odds then his time will surely come.

The German is a very confident character and is very personable and popular. He doesn't take himself too seriously but he takes his job seriously and that is a breath of fresh air in the paddock.

If Vettel was crowned world champion it would cap an extraordinary introduction to F1 and would strike a blow for the young talent on the grid.

Last season, McLaren adopted a very cautious approach to the race as all Hamilton had to do to deny Massa was to cross the line in fifth - in the end they only managed to take the title by the skin of their teeth.

Button has also talked about not needing to take any risks but Ross Brawn won't want to go down the same route.

There is no finer F1 conductor than Ross Brawn but the stakes are high and a lot will be asked of Brawn, Button, Barrichello and Vettel if the rain sweeps across Sao Paulo on Sunday.