Red Bull still puzzled by Singapore failure

The Milton Keynes-based team have conducted a thorough examination of Webber's gearbox after the problem forced him out of the race at the Marina Bay circuit - and cost him a podium finish.

But neither their analysis nor that of third-party suppliers have provided a satisfactory explanation for why the gearbox tried to select two gears at once.

Suspicions about outside interference were prompted, however, after the sister car of Scuderia Toro Rosso's Sebastien Bourdais suffered a similar gearbox failure in Friday practice at almost the exact same location on the track - the run from Turn 12 to Turn 13.

The theory about metro tram interference has resulted in the team examining detailed maps of the Singapore track area to judge whether a passing train could have played a part.

That analysis shows that underneath the location where the failures on both cars first occurred is the path of the East-West Metro Line - where trains run every 12 minutes.

Red Bull Racing team principal Christian Horner said: "The post mortem on the gearbox is it is a complete rogue failure. Obviously components have gone back to third parties for inspection too - which they cannot explain either. It is frustrating.

"At the moment we cannot say specifically what caused the failure, whether it was caused by the bumps or whether it has been caused by static interference.

"It is easy to look at circumstantial evidence and put the blame somewhere else, but we are not pointing any fingers. It was our first gearbox failure of the season and we have to make sure we don't have another one."