New Zealander Hartley was taken to the medical centre for checks after a sudden front left suspension failure on the Wellington straight pitched the car at speed into the barriers at Brooklands, bringing the session to a halt.
While Hartley -- merely a passenger as the car crossed the gravel -- was passed fit to continue, the damage to the car made it doubtful that he would be able to take part in qualifying.
"He's a bit shocked, but OK," said French team mate Pierre Gasly, whose car was thoroughly checked afterwards for signs of any similar problem.
The session resumed after a 13-minute stoppage.
Hamilton, winner for the past four years at Silverstone and five times in total, topped the timesheets with a lap of one minute 26.722 seconds.
Ferrari's Kimi Raikkonen was second fastest, 0.093 off the pace, with Hamilton's Mercedes team mate Valtteri Bottas third but 0.642 slower than the Briton.
Ferrari's Sebastian Vettel, who was suffering a neck problem, was fourth fastest and more than a second off Hamilton's time.
The Red Bulls of Max Verstappen and Daniel Ricciardo were fifth and sixth.
(Reporting by Alan Baldwin, editing by Clare Lovell)
