To add some extra detail... the a/c was apparently being towed on to a '
wash stand' for some washing of the engines. (
uhm, slippery when wet perhaps? 
)
Approaching the stand it's muted that the tug 'jackknifed' (
with all manner of speculation as to why?!) and that the a/c then impacted with the tug... therein causing substantial damage to the skin / frames on the RHS (in the area aft of the nose cone).
The aircraft is not in a flyable condition and so has to remain at LGW until the repair is complete.
To repair it, the damaged area will need completely re-skinning / re-framing, which apparently involves removal of the forward galley, much of the avionics / E&E bay, flight deck, etc... and following this it will need to be air-tested and the repaired area will need painting.
Boeing are sending over a substantial team of people (24?) to do the repair work.
With good fortune the a/c
might(?) be back in service prior to Christmas (
if only so that the Boeing team can be home themselves in time for the Xmas 
).
Guestimates at the cost of the repair are muted as being in the region of $2,500,000 USD !
with the assumption that the nose gear / torque box is not damaged?... in which case it'll take longer & cost more!