Button completed another relatively trouble-free day of running for the Woking-based team on Wednesday, recording 121 laps and posting the fifth best time.

And the Briton says the improvements Honda has made to its power unit after a troubled first week of testing at Barcelona were noticeable on his return to the cockpit.

Asked by Motorsport.com about the step in performance, Button said: "It's the biggest improvement I've felt with the power unit in the last 14 months, which is good!

"The improvement is good, but obviously we're still a long way off the other guys. You can see that in the speed traps, but you can definitely feel the difference on the initial part of the straight.

"It's positive, I think the important thing is we were able to do quite a few laps. We were held up a bit by some niggles, some red flags, but we've got that reliability which is important."

Set-up focus needed

Button nonetheless admitted that the team had yet to focus much on honing its set-up, which he said would be crucial in order to prepared for the season-opener in Melbourne.

"I don't feel we've done any proper work yet with the set-up, it's been mostly aero work and understanding if we're in the right place or not," he said. "Not specific driver set-up work.

"The next two days it will be fine-tune the car and find a balance that really works. We're not there yet, we need two really good days to feel ready for Melbourne."

Speaking about McLaren's place in the competitive order, he added: "I'm hoping we won't be hanging off the back.

"There's still a lot of work before I feel we are properly competitive, in the next two days to find a set-up that works for us."

Additional reporting by Jonathan Noble