Jenson Button believes that Mercedes are "miles ahead" of their competitors heading into the start of the 2015 season.

The Silver Arrows have largely been untouched by reliability problems that have hampered other team's development, including Button's McLaren outfit, and the Briton has suggested that the chasing pack are not catching up any time soon.

"Mercedes are unbelievably quick and we are a long way off," he is quoted by Crash.net as saying. "I'm not sure what fuels were being run, but Sauber and Williams were a massive chunk off them. It's all a guessing game though.

"I don't really know where anyone is and the only way to see is looking at the long runs which is very interesting, obviously the Mercedes is miles ahead. Some teams you can see real degradation."

Mercedes won the 2014 constructors' title by 306 points from Red Bull.