So did you ask CAA UK if they will accept to do this?
Initial instrument rating is different than renewal regulations. For renewal you can do in any country, first time IR I doubt it!
You need to get personal confirmation, not just reading standard information on their websites. Nothing is assumed, you need to make request.
Don't think CAA UK will accept initial IR from Iceland, but than again I might be wrong. From what I recall CAA UK have a few schools outside that they have pre-approved the training, where they will accept training.
Call CAA UK, and see what they tell you!