Hamilton's super-soft tyre time of 1:28.063s is quicker than what Mercedes team-mate Valtteri Bottas managed in First and Second Practice. It was just three hundreds faster than Vettel's Ferrari and 0.074s quicker than Bottas.
Kimi Raikkonen was fourth, but over a half off the pace, with Nico Hulkenberg a surprisingly ahead of both Red Bull's in fifth, but 1.4s slower than Hamilton.
Romain Grosjean was the meat in the Red Bull sandwich in seventh, Daniel Ricciardo ahead, Max Verstappen behind as Felipe Massa and Stoffel Vandoorne rounded out the top 10 positions.
Threat of rain sees early running
The possibility of a shower meant the in the early minutes of the 60 minute session, there was a lot of running, as teams tried to finish all of their practice programmes.
It was Bottas who topped this early part of the session, a soft tyre shod time of 1:28.827s being enough, before Hamilton's own soft timed lap brought a result of 1:28.747s.
That was the fastest soft tyre time, as the teams then switched to the high performance qualifying runs earlier than usual to ensure they were completed before track conditions became less than favourable when the rain did come.
On the super-soft Pirelli tyres, Hamilton was able to produce a 1:28.063s, which first Vettel and Bottas both failed to improve on, Vettel by the 0.032s margin which secured him second in the session and Bottas evantually by 0.074s, having whittled that down from nearly two ten tenths.
Rain catches Verstappen out
Verstappen did not complete a timed lap in dry conditions on the super-soft tyres, after Red Bull left it too late to send him out, leading to abort his lap at Brooklands.
The rain also prevented Carlos Sainz Jr and Lance Stroll from completing a timed lap on the super-soft positions, their finishing positions of 17th and 20th not being reflective of their car's pace.
As the rain did come down in the final moments, all 20 drivers headed out to get a feel for track conditions, with Ricciardo and Sauber's Marcus Ericcson, who occupied 19th place, both spinning.
|6.||Daniel Ricciardo||Red Bull||+1.549s|
|8.||Max Verstappen||Red Bull||+1.841s|
|12.||Esteban Ocon||Force India||+2.109s|
|15.||Sergio Perez||Force India||+2.353s|
|16.||Danill Kvyat||Toro Rosso||+2.441s|
|17.||Carlos Sainz Jr||Toro Rosso||+2.452s|