Should certain criteria be met within our SOP, we may nominate our destination LHR as the alternate as well, as it has two independent/2 different runways- runway ILS. We will arrive with our no delay (20 minutes holding fuel at BIG) and then commence the approach. Should for some reason we have a go-around/missed approach, we may return to LHR as opposed to setting course to LGW on a clear blue sunny day. Makes sense doesn't it.
This is when strict criteria is upheld that we may elect our destination as our alternate on the basis that two independant runways and ILS are available and we are not talking about a reciprical runway as this wouldn't work with wind or runway blockage.
A4, I hope this tries to clear an earlier point you didn't seem to understand. This decision to elect the destination is decided within one hour of arriving at destination and not at the last minute. It is caculated and planned as has the last 12 hours to get to LHR.
