I am going to try and make it. Just happens that I am in London that week (fist time in the UK!), and am planning to make the trek from London to Silverstone on Sunday, but without a car. What information I can find on the web says it is doable by train, but might be a pain.
Train to Northampton and taxi (or bus route) from there to Silverstone?
I suppose they won't have the shuttle buses from Northampton to Silverstone like for the GP weekend?
Any advice on getting there from London is appreciated!