Rookie title leader Marc Marquez, winner of the past four races, began the British MotoGP weekend on top, by leading opening Friday practice at Silverstone.
Completing his first ever laps of the fast Northamptonshire circuit on an RCV, Marquez took over at the top from Jorge Lorenzo
at the half-hour mark of the 45-minutes.
Marquez finished the session with an advantage of 0.219s over Yamaha's reigning double world champion.
Home star Cal Crutchlow, injured in both his previous British GP appearances, claimed a late third place for Monster Yamaha Tech 3, with a lap time just 0.228s from Marquez.
A gap then followed to Dani Pedrosa
(+0.615s) in fourth, with last year's pole sitter Alvaro Bautista (Gresini Honda) and Lorenzo's team-mate Valentino Rossi
completing a top six covered by 0.866s.
Stefan Bradl was seventh quickest for Honda LCR, with Nicky Hayden
the top Ducati in eighth, home rookie Bradley Smith (Tech 3) ninth and Andrea Dovizioso
CRT leader Aleix Espargaro set the privateer pace in eleventh place (+1.709s), while Ulsterman Michael Laverty began his and the PBM team's home weekend with 21st - out of 23 riders - in FP1.
Marquez starts this weekend with a 26-point title lead over Pedrosa and a 44-point advantage over Lorenzo.
Ducati test rider Michele Pirro is again replacing the re-injured Ben Spies at Pramac. Cardion AB's Karel Abraham is also absent through to injury, but has not been replaced.
FP2 takes place this afternoon.Free Practice 1:
1. Marc Marquez
2. Jorge Lorenzo
3. Cal Crutchlow
4. Dani Pedrosa
5. Alvaro Bautista
6. Valentino Rossi
7. Stefan Bradl
8. Nicky Hayden
9. Bradley Smith
10. Andrea Dovizioso
11. Aleix Espargaro
12. Andrea Iannone
13. Hector Barbera
14. Randy De Puniet
15. Colin Edwards
16. Michele Pirro
17. Hiroshi Aoyama
18. Yonny Hernandez
19. Danilo Petrucci
20. Claudio Corti
21. Michael Laverty
22. Bryan Staring
23. Lukas Pesek