Jenson Button insists that there is no reason for panic, despite having seen his F1 World Championship lead cut to just 21 points following last weekend's German Grand Prix - but he acknowledges that if Brawn GP's performance does not pick up considerably in the hotter conditions expected for the forthcoming races, 'we have got to really worry'.

The Mercedes-powered BGP 001 suffered in the cooler conditions at Silverstone and the N?rburgring, with both Button and team-mate Rubens Barrichello experiencing great difficulty in warming their tyres up sufficiently to be able to take the fight to dominant Red Bull Racing duo Mark Webber and Sebastian Vettel, with the energy drinks-backed outfit remaining unbeaten and unrivalled in the last two outings.

Whilst Webber and Vettel have notched up 18 points apiece, Button's tally from Britain and Germany was just seven, and the long-time 2009 pace-setter admitted that he has had more enjoyable days than that which he experienced around the Eifel Mountains circuit on Sunday.

"It was a really frustrating, difficult race," the 29-year-old told the BBC. "I got a really bad start - off the line I wasn't good, and in turn one I had cars all around me. People were out-braking themselves and everything, and it would have been so easy to lose a front wing; I almost did, so I had to back out of it and I think I was about eighth after turn one.

"I got a few cars back round the outside which was nice, and I got up to fourth past [Felipe] Massa and was behind [Heikki] Kovalainen, but there was no way past and his pace was way off. I then got up behind Rubens. He had a bad second pit-stop, because he came out probably about four seconds in front of me when he had been about eight seconds up the road, so he lost the opportunity to finish where I don't know. His pace on the 'Prime' tyre wasn't very good, and I was stuck behind him for quite a few laps, so it was a tough one.

"When the circuit cooled down it got a lot harder. The Prime tyre was difficult to heat up; I was doing quite a lot of weaving, and that helped me quite a bit, but I couldn't keep the heat in the 'Option' tyre and that was the problem. You slide the tyre and it starts graining, and I had big degradation. I had thought we'd have a chance of getting a podium behind the two Red Bulls, but that wasn't possible."

Indeed, not only did Brawn get beaten by chief title rival RBR in Germany, but the ex-Honda F1 outfit similarly found itself outpaced by both Ferrari and Williams, with Fernando Alonso in the resurgent Renault also threatening to depose Button and Barrichello before the race was through.

The recent results have enabled Red Bull to close the gap separating them from Brawn from 43.5 points to just 19.5 over the course of the last three grands prix, with 144 remaining up for grabs between now and season's end. What's more, Vettel and Webber are closing inexorably in on Button in the drivers' standings too, where 80 points are still available.

Brawn is expected to be back on the leading pace again in the anticipated warmer climes of Budapest in just under a fortnight's time, with the tight and twisty layout of the Hungaroring also tipped to suit the car down to the ground. If his dreams of championship glory are not to crumble before his eyes, Button warns it will have to.

"We've got to kick some a*se in Hungary, and that's what we are going to try and do," the Frome-born ace - who achieved his breakthrough F1 victory in the very same race three years ago - is quoted as having said by Reuters. "Let's pray that we are quick there, because if we are not we've got a problem.

"There are a lot of races to go, so we do need to worry a bit. These two circuits (Silverstone and the N?rburgring) have been frustrating for us because of the temperatures. If we are not quick on a hot track then we have got to really worry, [but] I think our car will be strong there. We don't know how strong; we'll have to wait and see.

"We could shout at the team about improving things, but they know what they've got to do. We've got to stay calm, put the improvements on the car and get every bit we can out of it. You have to worry, but I don't think it's 'oh sh*t, we're going to lose the championship'. It's 'come on, let's make the difference'."

One factor that the British star did point to was that Webber's N?rburgring triumph - his first in the top flight after 130 attempts - has added another name to the equation in terms of the chase for the crown. Button acknowledged that the Australian's challenge could in fact arguably play in his favour, in making it four drivers taking points off each other rather than just three, potentially protecting his advantage for longer than would otherwise have been the case.

"It puts another person in the mix, doesn't it?" he mused. "Sebastian, Mark and Rubens - they are all closing in on me. We've still got a 21-point lead so it's not that bad, but if we continue like this we are not going to keep that lead. It's a different person in second now, but he's got his team-mate right behind him, which is probably a good thing for me because they're both taking points off each other.

"If Vettel had won here it would have been a disaster, [but] I'm looking forward to Hungary. Hopefully we've got a few new parts and it's going to be hotter - and we really do need to beat the Red Bulls in Hungary! I'm not going to put any pressure on the team, though, because we know what we've got to do - and we'll do it in Hungary."