Jenson Button quickest in rain-hit first practice for the German Grand Prix

The Briton's 1m16.595s lap was 0.498s faster than his team-mate Lewis Hamilton, with championship leader Fernando Alonso third on the timesheets for Ferrari.

Intermittent rain showers rendered times fairly irrelevant in terms of determining form, with teams frequently having to cut short evaluation runs for the updates they have brought to Germany. Button's time was set when the track was completely dry in the first 20 minutes of the 90.

Of the established runners, only he and Lotus driver Romain Grosjean got their programmes running before precipitation played its part.

When Sergio Perez, Mark Webber and Heikki Kovalainen all then ran wide, however, it was a clear signal that the asphalt was no longer dry and this set a pattern for the rest of the session.

With short, sharp showers dampening the track and then warm ambient temperatures quickly drying it again, the surface became dry enough for teams to continue, if somewhat stutteringly, with their programmes on the medium and soft compounds. During this point, Nico Hulkenberg and Alonso improved to go second and third behind Button.

Unsurprisingly, almost every driver had a moment at some point as the grips levels changed constantly.

The heaviest of these showers came 20 minutes before the end, prompting Sauber's Perez and Kamui Kobayashi - who had a significant moment running across the gravel early on - to try intermediates. That plan was swiftly scuppered though after an exploratory lap each.

The last 10 minutes provided some of the driest running and also a flurry of activity on the timing board as Hamilton went second quickest to make it a McLaren one-two. Alonso improved again to go third with Michael Schumacher's Mercedes fourth.

Perez also squeezed ahead of Hulkenberg before Valtteri Bottas crashed Bruno Senna's Williams at the Sachs Kurve with three minutes to go. That scuppered any hope of anyone going quicker through the final sector - including Hamilton, who was fastest of all through S2 on his final lap.

Nico Rosberg was seventh ahead of Felipe Massa, Pastor Maldonado and Grosjean.

The Red Bulls had a low-key session, with world champion Sebastian Vettel 12th and Webber 20th. Kimi Raikkonen was 15th in the Lotus, running with the new double DRS system, having only completed 14 laps in total.

Pos  Driver                Team                    Time              Laps
 1.  Jenson Button         McLaren-Mercedes        1m16.595            27
 2.  Lewis Hamilton        McLaren-Mercedes        1m17.093s  + 0.498  22
 3.  Fernando Alonso       Ferrari                 1m17.370s  + 0.775  21
 4.  Michael Schumacher    Mercedes                1m17.382s  + 0.787  20
 5.  Sergio Perez          Sauber-Ferrari          1m17.413s  + 0.818  28
 6.  Nico Hulkenberg       Force India-Mercedes    1m17.599s  + 1.004  17
 7.  Nico Rosberg          Mercedes                1m17.915s  + 1.320  27
 8.  Felipe Massa          Ferrari                 1m17.995s  + 1.400  22
 9.  Pastor Maldonado      Williams-Renault        1m18.020s  + 1.425  20
10.  Romain Grosjean       Lotus-Renault           1m18.130s  + 1.535  21
11.  Kamui Kobayashi       Sauber-Ferrari          1m18.226s  + 1.631  22
12.  Sebastian Vettel      Red Bull-Renault        1m18.339s  + 1.744  21
13.  Valtteri Bottas       Williams-Renault        1m18.422s  + 1.827  28
14.  Daniel Ricciardo      Toro Rosso-Ferrari      1m18.709s  + 2.114  30
15.  Kimi Raikkonen        Lotus-Renault           1m18.831s  + 2.236  14
16.  Jules Bianchi         Force India-Mercedes    1m18.972s  + 2.377  21
17.  Jean-Eric Vergne      Toro Rosso-Ferrari      1m19.039s  + 2.444  34
18.  Vitaly Petrov         Caterham-Renault        1m19.674s  + 3.079  24
19.  Heikki Kovalainen     Caterham-Renault        1m19.963s  + 3.368  24
20.  Mark Webber           Red Bull-Renault        1m20.122s  + 3.527  27
21.  Charles Pic           Marussia-Cosworth       1m20.169s  + 3.574  20
22.  Timo Glock            Marussia-Cosworth       1m20.539s  + 3.944  18
23.  Pedro de la Rosa      HRT-Cosworth            1m21.138s  + 4.543  24
24.  Dani Clos             HRT-Cosworth            1m21.740s  + 5.145  27

All Timing Unofficial