Carlos Sainz believes both McLaren and engine supplier Renault have made solid progress over the winter after setting the fastest time on Wednesday.

The Spaniard managed the fastest lap of pre-season testing to date with a 1m17.144s, that lap coming on the C4 Pirelli tyres, the second softest compound in the range.

It is also a lap that has raised some eyebrows as it puts McLaren on the same level as Ferrari and Red Bull when tyre-corrected, and Sainz believes this is just the start for the British team.

“There’s still big areas for improvement, definitely,” he told reporters in the paddock. “The important stuff to come out of these seven or eight hour days is every time I’ve been on the track, in the car, I think it’s been progressing.

“The car balance has got better over the last few days, and that is allowing us to extract a bit more from it, so it means the team is working well.

“We are understanding the underlying balance issues and correcting them little by little, but still there is a long season ahead and big areas of improvement where we need to keep working.

“We are still not where we want to be. This is definitely the right answer and we need to keep working hard.”

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The former Renault driver also backed up claims that the French manufacturer has made strong gains with their power unit.

"It feels like a good step, that's the only thing I can say," Sainz told GPFans.com.

"Until anyone turns up the engines in Australia and we see the top speeds, it's going to be very difficult to find out how good the step is, or if the others have made a step as big as we have done.

"My initial guess is: I feel it, I feel a big step on the engine and it's going in the right direction."

Despite the optimism, Sainz admits it is very unlikely this signals McLaren will be back competing high up the grid.

“A 17.1 around Barcelona is fast,” he said, “but I guess teams like Ferrari and Red Bull can go faster than that. So I’m very cautious and calm.”