If recent rumours are to be believed, an increasing tension has crept into the relationship between Red Bull Racing's team-mates.

With the exception of the Brawn duo, Sebastian Vettel and Mark Webber occupy the best car in the 2009 field, and their battle for third in the drivers' title is separated by just 1.5 points.

After finishing behind his more experienced team-mate in Turkey two weeks ago, Vettel was clearly unhappy that his championship charge had been road-blocked by the Australian.

"I don't think there is tension between Mark and Sebastian," David Coulthard, Webber's team-mate last year and now a consultant to the Milton Keynes-based team, said.

The Scot, speaking from Lima, Peru, where he demonstrated an F1 car, said inter-team rivalry is just a normal part of the sport.

"Of course you can't have two winners, so by definition if your team-mate is winning then you are losing. But that is a relationship that has always been the case in Formula One," Coulthard explained.

Writing in his latest column for the BBC, meanwhile, Webber admitted that trying to beat the highly rated 21-year-old is a source of great motivation.

"It's the first time I've had someone so quick as my team-mate, and I've always said that's what it's all about - at this level, you want to compare yourself to the best guys," he said.

"Vettel is hot property at the moment and he's done a great job to get where he is but there's just a point and a half between us in the championship.

"People ask me if I feel under pressure, but I think there's more pressure on Sebastian. In people's eyes, I'm not supposed to be doing what I'm doing. People think he's the new Schumacher and should be hosing it, but it's good that's not the case," added Webber.

He said their relationship is intact even though they are both trying to get the upper hand.

"The last two or three races have gone well for me and less well for Sebastian but things are fine between us," said Webber.

He insists it is too early in the season for Red Bull to select one driver to push for the drivers' title.

"You could throw it all in with Sebastian but he crashed in Monaco so you've still got to give both cars the best chance to get the best result possible," he concluded.