If you want to switch all on using the switch.
At the ceiling rose you will have four terminal points:
Which could possibly look like this
Live (which will have 2 ports, where the brown flex of the lamp and black or blue of your lighting circuit are terminated, normally identified with a red or brown sleeve over it.)
Neutral (3 ports, where blue flex of lamp and blacks or blues)
Loop (central terminal, where all live cores are terminated reds or browns)
Earth (CPC/Earths terminated, yellow/green)
If you wish the same single switch to operate this and new spots, run a 2 core and earth across them.
Connect the earth/CPC to that terminal on the rose, then the blue core to the neutral terminal of spots and neutral terminal of rose and the brown to the live terminal of spots and live terminal of rose(not the loop) if there are three individual spot lights, repeat this process across all of them earth-earth neutral-neutral and live-live terminals.
If the spots have transformers the cables are connected across the neutrals and lives of these, still connect your earths in a connection block to keep continuity.
Any joints of cables within the ceiling void must be accessible, so if these lights are downlights with transformers, the transformers and joints must be accessible through the hole made for the downlights.
Also if you must take in to consideration the spread of fire within the ceiling void, if there is living space above lights should be fire rated or have fire hoods.