Lewis Hamilton has told Jenson Button not to expect any favours in the fight for the world championship.

The two drivers may share an allegiance to the British flag, but Hamilton has insisted they will not be brothers in arms when they take to the starting grid for Sunday's European Grand Prix in Valencia.

The return to form of McLaren, confirmed by Hamilton's stunning victory in Hungary last month, could be a huge boost for Button as he attempts to defend an 18.5 point lead over Red Bull's Mark Webber in the chase for this season's title.

With reigning champion Hamilton now in the hunt for more wins, it is likely to be harder for Australia's Webber to make substantial gains on Button in each of the remaining seven rounds.

But Hamilton has dismissed any notion that he might deliberately help his countryman maintain his advantage. He said: "I'm not really looking to do that. I'm looking to win races for us as a team and for us to be as successful as we can be.

"If that happens to help Jenson win the championship, then that would be fantastic for me and for all British fans. But he's not my team-mate and I'm not here to help him win. We're here to win races ourselves.

"The greatest thing, I think, is if I was to be very competitive at this last bunch of races. It's great for people to see that we still have it and that I am still a worthy world champion."

Button needs to respond to the growing challenge from Webber by ending a run of three disappointing performances with a return to the podium.

Brawn team principal Ross Brawn and his engineers have spent much of the four-week break since the Hungarian Grand Prix pouring over data in a bid to discover why they have lost their edge, particularly in the area of tyre grip.

Despite the setbacks Button remains positive. He said: " I think we have just maybe gone slightly in the wrong direction. But we will pick up our pace, for sure. We need to be on the podium as often as possible. But it is very, very competitive now.

"You haven't just got the Red Bulls who are strong. You have got the McLarens, the Ferraris, the Renaults and even the Williams have been competitive. We need to get back on top of it. I have got that 18.5 point lead, but that could disappear very quickly."

The Ferrari challenge has been weakened by the absence through injury of Felipe Massa and the failure of Michael Schumacher to prove himself fit enough to make what would have been a sensational comeback from retirement. Massa's car will now be driven this weekend by their test driver, Italian veteran Luca Badoer.