Pinewood is a legendary production studio based in London with an impressive roster of movies that have been filmed there. Most notable productions include all the Harry Potter films, Hunger Games films, Bond films, Star Wars films, and a few Marvel movies. With Marvel releasing movies twice a year and the Star Wars franchise doing the same after 2015, Industrial Light & Magic wants to move effects production closer to Pinewood studios and is opening a London effects facility. With the increasing complexity and volume of effects work required for these large budget films, this seems like it was inevitable.
For the full details on the fiscal and logistical reasons behind ILM's opening in London (things like UK tax credits), check out THR.