This looks like a good first cycle Azorean Gull which was found in Iceland a few days ago.
Note the overall dark impression, with ghost hood, almost plain dark coverts, dark shin pads, loose textured coverts, plain dark tertails, dark blotched underparts and in flight with very contrasting white tail coverts against a broad dark tail band with thick widely spaced bars on the undertail coverts. This particular individual is rather retarded but this could be explained by it's vagrant context.
Here's a few more first cycles from the Azores here:
Compare this Iceland vagrant to other Atlantic Yellow-legged Gulls which overall show more resemblance to michahellis.
First-cycle Azorean Gull has a rather distinct plumage which carries a diagnostic suite of features and is quite dissimilar to other Atlantic Yellow-legged Gulls.