The replays suggested a front-left tyre suspension failure with Hartley crashing into the barrier heading into Brooklands. The left front suspension failed as soon as the Toro Rosso driver hit the brakes and he couldn't slow before running into the gravel trap, flipping, and hitting the barriers.
Raikkonen and Hamilton spent the remainder of the session swapping times at the top of the order, but a 1m26.722s from Hamilton in the closing stages of the session put the Brit just out of reach.
The Silverstone circuit is one of the fastest on the F1 calendar.
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The Red Bulls of Max Verstappen and Daniel Ricciardo rounded out the top six, but only after an unexpected challenge from the Sauber of star rookie Charles Leclerc. That left the New Zealander powerless to stop his vehicle flying across the gravel and into the barrier.
Hartley was able to walk away from the wreckage but was given a check-up at the Medical Centre as a precaution. His teammate, Pierre Gasly, will start 14th.
The red flag was immediately waved on the session and there was a 14-minute delay as marshals cleared the wreckage with Hartley's vehicle being craned away. The considerable damage to the vehicle meant that Toro Rosso was unable to get it out for the afternoon's qualifying session This leaves Hartley all the way down the order in twentieth place.