Preppy, CAP513 also states:
"It is, therefore important that any aerodromes designated as en-route alternates should have the capabilities, services and facilities to safely support that particular aeroplane........
.......these considerations shall apply to all aerodromes which are considerd as alternates during the ETOPS segment, thus possibly include the departure and/or destination aerodromes."
I do not believe that this aircraft was flying the ETOPS segment therefore CAP513 doesn't apply to diversions outwith the ETOPS portion of a flight.
The CAP513 definitions of suitable therefore do not apply here. If they did, then suitable could be for engineering and/or passenger comfort purposes