Sebastian Vettel admits Red Bull have found it difficult to improve their performance and bridge the gap to runaway championship lead­ers Mercedes over the first half of the 2014 season.

The Milton Keynes-based team have dominated in the construc­tors’ standings for the past four seasons, but over the opening nine races of the year have scored just over half the points total of the Sil­ver Arrows.

Both Daniel Ricciardo and Vet­tel, meanwhile, are more than 60 points behind Mercedes’ pairing of Nico Rosberg and Lewis Hamilton.

While the Red Bull duo have en­joyed various successes this year – most notably Ricciardo’s triumph in Canada – Vettel admits Red Bull have not made significant inroads into their deficit to Mercedes in the constructors’ standings.

“Right now the gap is very big and we haven’t really closed the gap since race one,” Vettel, who has scored podiums in Malaysia and Canada, told reporters at the just-concluded Silverstone test.

“It has been up and down this year. Obviously we have tried lots of stuff to improve, but they (Mer­cedes) are doing the same thing.

“We are waiting for bigger steps to happen to close the gap even more which I think at the end of the season we can judge a lot better – then we know what we can do over the winter.”

Asked what he hoped to achieve next weekend at his home Grand Prix in Germany, Vettel said break­ing into the top three was his chief focus.

“Obviously we hope for a smooth weekend without any problems, and to try and get the best out of myself and the car,” he said.

“It would be very special to finish on the podium there,” he added.