Having been at this business for a very long time, I can appreciate both sides of the question...to continue or divert.
NoD makes a very compelling argument for continuing, and I would normally agree, provided diversion options remain plentiful.
However, having said this, I would not, except under the the most unusual circumstances, continue a long overwater crossing, where the next available could well be rather far away.
To do so would be foolhardy, in my opinion and, quite frankly, suspect it would definately be frowned upon by the FAA.
It does seem odd that the UKCAA (and their predecessor, the ARB) would be so stringent about the handling/stall characteristics of large jet transports, yet allow these rather long flights with an engine inoperative.
I can well remember the FAA inspector when I received my first jet type rating (B707) looking me straight in the eye and saying...'remember, the 707 will fly quite nicely on three, but it does not mean that you should do so for an extended period.'
I quite frankly do not believe any differently thirty years later.