hi james,
give me a call tomorrow on 0789 007 3260, i am either travelling from portsmouth (goes via 3 bridges), from crawley or from smartparts (which is close to bromley) - depending upon when our new tops arrive.
if you drive then early morning drive round M25 then up the m11 towards the airport.
if you take the train then there is two options - spend a night in a london station or spend the night in the airport (this is what portsmouth is doing)
i have all the details for both, but if you are thinking of an airport taxi link it is expensive, if you do this i may be up for sharing, again call me.