Agree with BullHead, unless you can be there at stupid o clock to queue for gates opening (and some people sleep in the queue all night), which will be difficult using public transport the best General Admission spots will be taken.
I haven't been by public transport myself but they do run special trains and buses for the Grand Prix so it is possible.
For example Bus:https://uk.megabus.c...rstone2013.aspx
(runs all 3 days)
Departs 07:30 London ,Victoria Coach Station Arrives 10:00 Silverstone ,Car Park West 4 £14.50
Departs 16:30 Silverstone ,Car Park West 4 Arrives 19:00 London ,Victoria Coach Station £14.50
Train: http://www.silversto...h.0W2v6SxE.dpuf
Virgin Trains are running a dedicated service for British Grand Prix goers on Sunday 10th July to Milton Keynes from London Euston, you will then get a coach transfer (included in the ticket price) to Silverstone. The coach transfer will take approximately 30 mins to and from the car park located near the main entrance.
Outbound Train Service Outbound TrainConnecting Shuttle
08:10 - 08:55 London Euston to Milton Keynes Central 09:10 - 09:45Milton Keynes Central to Silverstone Circuits
08:20 - 09:05 London Euston to Milton Keynes Central 09:20 - 09:55Milton Keynes Central to Silverstone Circuits
08:45 - 09:31 London Euston to Milton Keynes Central 09:46 - 10:21Milton Keynes Central to Silverstone Circuits
Return Train Service Connecting Shuttle Return Train
17:00 - 17:35 Silverstone Circuits to Milton Keynes Central 17:50 - 18:27Milton Keynes Central to London Euston
17:09 - 17:44 Silverstone Circuits to Milton Keynes Central 17:59 - 18:38Milton Keynes Central to London Euston
17:14 - 17:49 Silverstone Circuits to Milton Keynes Central 18:04 - 18:44Milton Keynes Central to London Euston
London Euston - MK Central - £50 per person return