Mercedes holds fire on engine plans

The FIA told teams in December that in-season upgrades were now allowed, following a challenge from Ferrari that the regulations had failed to specify an exact date for delivering them.

The clarification means that manufacturers no longer have to ensure they have done all their work by the season-opening Australian Grand Prix - as had been the original idea.

Despite the fact that there is now more time to bring upgrades, Mercedes says that its 2015 plan remains unchanged - and that it will only commit to its programme when it knows how pre-season running has gone.

Mercedes engine chief Andy Cowell said: "This decision hasn't altered our development strategy for 2015, which was always to gather the necessary data from pre-season testing in order to define and submit the engine specification for the opening race.

"However, it does offer the opportunity to exploit this interpretation for further gain later in the season, should we choose to do so."

Mercedes could choose to hold fire on a number of potential improvements if it feels that it has enough of an edge early on. That could help deliver a bigger performance boost for the crunch phase of the title battle.

The team began proper testing of its new W06 at Jerez in Spain on Sunday, with Nico Rosberg setting the early pace.