London is such a large place that travel times depend on whereabouts in London you start, and what time of day. A fair approximation would be 2 - 3 hours. More if you start in east London, or travel during the rush hour.
You can't travel directly from Amsterdam to London by ferry because London doesn't have a ferry port. You would have to travel from Amsterdam to Hook of Holland by train (or drive), catch a ferry to Harwich and then take a train (or drive) to London.
It is not possible to drive from London, United Kingdom to China. A flight would take about 10 and a half hours to fly on a commercial airline.... Once you have crossed the English Channel (in your car) it's perfectly possible to drive to China.