Considering how often Apple gets sued for patent infringement by "patent trolls", I would expect they've done their due diligence to ensure that they have removed any proprietary Imagination IP from their design. As
cmaier noted, it is up to Imagination to prove that Apple is illegally using their IP. If they feel they have a case, they'll sure when Apple launches their first GPU after the license agreement is terminated.
The Rule of Law still applies in the UK so I would expect if Imagination does sue in a UK court, the case will be adjudicated on the facts and not the local interest.
While Steve Jobs quoted Pablo Picasso about "good artists copy; great artists steal", Picasso meant that great artists learn from past masters, incorporating what they like into their own idea and creating something unique from it.
So Apple will have certainly learned from using Imagination's PowerVR IP under license on how to create a mobile device GPU, but they will not just simply copy it - which would be IP infringement. They will instead use it as the inspiration to create their own, unique GPU that does not infringe (in Apple's mind) on Imagination's IP.