The problem is that the exhibition centre ExCel is completely the wrong side of London from Putney and on a work night did not want to stay out too late.
But was rather surprised when, having run for trains, jumped on tubes as the doors were closing, managed to do the trip in "just" an hour. It reminded me of that Top Gear cross London race in which the bike won (though that journey was in the opposite direction).
However later measured the distance on Google Earth and calculated that works out as an average speed of 10 miles per hour.
Not sure that is much better than a hundred years ago!