Red Bull F1 boss says closing power deficit 'very difficult'

With a big push being made by teams to relax F1's engine freeze rules, Horner believes that the situation is still tough for Mercedes' opposition.

And he feels the matter is particularly frustrating for his outfit - having faced numerous changes to aerodynamic rules over recent years that were aimed at holding back its dominant form.

"It's very difficult because with the chassis, if you're behind, you have the opportunity to develop," he said.

"With the engine and this new technology, you're freezing immature technology and it's very difficult therefore for the manufacturers to recover.

"In the last few years there were regulation changes to try and slow us down, whether that was blown diffusers, double diffusers, flexible body work, engine mapping, the goal posts were always changing.

"Whereas with the engine, it's a frozen untouchable element so it's very difficult to reduce that gap to your opponents."

Despite his frustrations about recovering the gap to Mercedes, Horner believes his team's 2014 campaign was one of its greatest success stories in Formula 1 - even though it lost out in the championship battle.

He believes that the way the team recovered from a disastrous pre-season testing programme was admirable.

"I actually think what the team has achieved this year is one of our biggest successes," explained Horner.

"When you consider where we started in the pre-season testing, then to be at this point in the championship, being the only team other than Mercedes to have won, and to have won three grands prix, to be second in the constructors' championship and third in the drivers' world championship.

"It's a remarkable come back from practically no pre-season and obviously the handicap of lack of horsepower that we have compared to the Mercedes-powered cars."