Some details from a photo on Flickr about the service and why the 92 is being pushed:
"92 015 & 92 036 are seen arriving at Dollands Moor International Freight Yard with train 4073 1100 Frethun Yard to Dollands Moor. The first train to run from China to London although its not the same train that left China because of different loading gauges which meant the containers were transferred from one set of wagons to another.
The train will have passed through China, Kazakhstan, Russia, Belarus, Poland, Germany, Belgium and France before crossing under the Channel and arriving in the east end of London at Barking rail freight terminal on Wednesday night/Thursday morning due to the fact the train is to heavy for HS1 so will go up in two portions, one Tuesday night and the other Wednesday night. The portions will be reattached and there will be a VIP ceremony with 92 015 to be seen "arriving from China" for the viewing guests although all with not be as it seems as the siding isn't "wired" and a class 66 will be pushing the 92 plus train from the rear!
Faster than a ship and half the cost of air freight everyone is hoping this service can entice customers to rail and start new growth in Channel Tunnel Freight services which are at such a low ebb nowadays.
92 015 will take the train up HS1 and has been spruced up for the event and launch of this service."