Valentino Rossi led a Ducati one-two during a wet opening practice for the British MotoGP
The first of the Friday sessions took place in soaking wet conditions almost identical to last year's Silverstone
Ducati riders Rossi and Nicky Hayden
were quick throughout the 45-minutes, although last year's winner Casey Stoner
also led the timesheets in the closing stages.
Repsol Honda's reigning world champion Stoner was ahead with two-minutes to go, when Hayden - who set the fastest lap in last year's race - burst 0.9s clear of the Australian on his final lap.
Rossi, who struggled badly on his Silverstone
debut last year before salving sixth in the race, then pipped Hayden by 0.077s on his own final run.
Seven time champion Rossi took his Ducati-best second place in similarly wet conditions at Le Mans this year.
Monster Yamaha Tech 3's Andrea Dovizioso
(+0.799s) bumped Stoner back to fourth, with team-mate and home hero Cal Crutchlow in fifth but almost two-seconds from Rossi.
Rookie Stefan Bradl, winner of last year's Moto2 race, began the weekend in a solid sixth, with Stoner's factory team-mate Dani Pedrosa
just behind the German in seventh.
Yamaha's newly re-signed world championship leader Jorge Lorenzo
was eighth for Yamaha and a cautious 3.8s behind Rossi.
Honda Gresini's Alvaro Bautista (ninth) and Factory Yamaha's Ben Spies (eleventh) walked away after falling towards the end of the 45-minutes.
The leading CRT rider was Frenchman Randy de Puniet, in twelfth place for Aspar Aprilia (+5.0s).
Cardion AB Ducati's Karel Abraham has been declared unfit to ride due to finger fractures in his left hand sustained during testing at Aragon.
Second practice takes place this afternoon.Friday practice (1):
1. Valentino Rossi
2. Nicky Hayden
3. Andrea Dovizioso
4. Casey Stoner
5. Cal Crutchlow
6. Stefan Bradl
7. Dani Pedrosa
8. Jorge Lorenzo
9. Alvaro Bautista
10. Hector Barbera
11. Ben Spies
12. Randy De Puniet
13. Mattia Pasini
14. Danilo Petrucci
15. Michele Pirro
16. Aleix Espargaro
17. James Ellison
18. Yonny Hernandez
19. Ivan Silva
20. Colin Edwards