It was called stores basin because all the supplies/logistics (Non armament and food) for the Royal Navy Far East Fleet were landed in that area where there were many godown type storage areas. There were also oil pipeline connections to each berth linked to the many tanks at Senoko which was the main storage area of fuel for the Fleet. Some tanks are still there and feed the power station I think.
There are two aircraft carriers if you look closely. One was HMS Victorious (full side on when you look). The other is actually at right angles to it in the basin itself (top left and adjacent to Victorious) It was actually a commando carrier with helicopters, most of which had been disembarked to one of the shore bases at the time. Hope this makes sense to you!
Eh …. Actually I am still unable to spot the second aircraft carrier. I trust that my readers are less dense than me. :(