While yesterday, having posted the fastest time - which was subsequently beaten by Charles Leclerc, Hamilton switched focus to longer runs, this morning, having initially thrown down the gauntlet, teammate Bottas responded to Vettel's challenge, but come the lunch break was still 0.340s adrift of the Ferrari's pace.

Admitting he is "not quite sure" what the gap to Ferrari is, the world champion told reporters in Barcelona; "I think it's potentially half a second... something like that, potentially.

"We will be analysing a lot from this test," he continued, "and there will be some mods that we try to implement. There's not a lot of time, hopefully we'll gain a tenth at least just on our understanding of the car.

"It's old now," he said of the W10, "it's worn and torn, so we'll have new components. All that stuff will come along. So, it's interesting."

Asked if that 0.5s gap might be reduced by the time the teams arrive in Melbourne, Hamilton admitted: "I have no reason to expect that...

"The testing, you have to take it with a pinch of salt," he continued. "We could get there and it could be bigger... we could get there and it could be less... we could get there and it could be equal. I really have no idea.

"There is no way when you are looking at the GPS to know what fuel load they are on, or what engine mode they are on," he admitted. "They are faster on the straights than us. Is that because they have their flexi wings that they have had in the past that drops drag, or are they more turned up than us, or are they more efficient and have less drag than us in general, or are we heavier? We have no idea we really won't know until we get to the race.

"Of course naturally we hope that it is definitely not bigger than what we might see now and we hope it is better. But we cannot bank on that so we have to work towards trying to close the gap that might be there, or is there."

Check out our Friday gallery from Barcelona, here.