The German car manufacturer's power unit has been the class of the field since the new turbo era came into force in 2014, and it has secured back-to-back championship doubles.

Although Mercedes' rivals may have hoped that the Silver Arrows had reached the limit of potential with hybrid V6 technology, engine chief Andy Cowell said on Friday that their engine still has plenty more to deliver.

"We've made some huge gains in the last years as we have done the development," he explained during a briefing with media at Mercedes' Brixworth facility on Friday.

"We have good gains over the past two years of racing. I don't see that stopping. I don't think anybody here sees that we have reached the limit.

"Where we are at today with our thermal efficiency is mind blowing when you step back and look at it."

Thermal efficiency

The new fuel-efficient F1 regulations have put a premium on thermal efficiency, which is effectively the amount of energy produced against the fuel delivered.

The more efficient the engine is, then the more power can be produced from a formula where fuel capacity and fuel flow rate are strictly controlled.

Cowell confirmed that the Mercedes engine was now delivering in excess of 900bhp.

Mercedes believes its power unit was delivering more than 45 percent thermal efficiency last year – and a graph shown to journalists suggested that the step being prepared for 2016 could be as big a leap forward as the team made between 2014 and 2015.

Cowell would not elaborate on the specific data to confirm that is the size of jump expected, but did hint that big chunks of power were still being unlocked.

"It will continue to go up," he said. "Does it get harder to find gains? Yes it does. But there are lots of areas where small gains will come.

"It is a bit like gold mining, you work bloody hard, you get lots of dust and now and again, you get a nice big nugget that makes you smile. And we still find those nuggets…."

He added: "Thermal efficiency is going up, from where we were in 2014 we took a good step up for 2015 – and perhaps it is going to go up in 2016.

"It is definitely going to go up in the future as well because nobody has said that we have reached the limit here. When I walk around the factory I never hear people say that is the best we can do, that is optimum…"

Honda threat

Despite optimism about the Mercedes unit, Cowell is well aware that rivals were chasing them hard, and even reckoned Honda needed to be watched closely.

"If we look at what Ferrari has done over the last 12 months, it's remarkable," Cowell said. "Their improvements have been a huge credit to their reshuffle and their enthusiasm.

"Everybody here is going 'I wonder how we're going to do?' Nobody here is assuming we are going to win, everybody here is assuming that we're going to get beaten by Ferrari, and Honda are a big threat.

"They have come in quickly and they are learning in front of the public but they're hugely determined and partnered with McLaren who are hugely determined.

"We know exactly how McLaren work in terms of a data-driven approach, so they are going to make some big, big gains.

"Renault's determination as well, as they've shown by being a lot more involved now in Formula 1, instead of just being a power unit provider there has been a team restructuring. There are going to be some great stories to talk about."