Why was only one cable used did the builder decide this?
Can the other cable be used for the EVSE, is your electrician conversant with EVSE installations?
You said you knew which one went into hole 1 if this is not the case under no circumstances guess because if you get it wrong you will create a dead short (one of the blacks is a live return from the switch).
If you are certain you know which black went into hole 1 then push it back in. The other two blacks go into holes 5 and 6. The green/yellow into 3 or 4 it doesn't matter which one.
I would say the dome part goes in first then the other silver part to clamp the cable braid or armour, then the rubber, brass washer and bush.
I would suggest trial and error but judging from your last post I suspect you don't have much patience.
It is not clear if it is off a ring final they do not say this and the fact a fuse box is involved it is not certain, the use of the term spur maybe misplaced who knows without more info.
Spur is the interesting word, is it spurred from a ring final because if so you may have problems or has the term spur been used to describe a separate supply to the fuse box.