This picture shows the usual arrangement in the UK for wiring a ceiling rose...
http://www.diydoctor.org.uk/project_images/ceilingrose/Untitled-1%20copy.jpg
You need to have four separate terminals to connect the various wires properly.
TURN THE POWER OFF
The quantity of wires you will have may vary but there's usually a power cable coming in - a cable that runs to and from the light switch - a power cable to the next ceiling rose in the house. As well as this there will be wires that attach the light fitting.
All the Earth wires connect together and to nothing else
All the Live wires (usually Red) connect together and to NOTHING ELSE not even the light!
One of the Black wires may look like a Neutral but it isn't - it's the return from the Light Switch and it's called Switched Live. It's special, scary and potentially dangerous because it's live when the switch is on and it's easy to confuse it as being a Neutral. For this reason it should have an identifying Red or Brown sleeve on it to show that it's Switched Live. This is the wire that delivers power to the light and lets you turn it on and off.
Once you've identified Switched Live, connect it to its own terminal - You will connect the Brown wire of the light to this wire (terminal strip) - just the two of them together and nothing else.
You will just be left with Neutral wires probably 2 Black ones and a Blue one that goes to the Light - connect them to the fourth and last treminal strip.
If you have trouble identifying Switched Live nip out and buy a Mains Tester Screwdriver with a Neon in the handle - jolly useful and very cheap - get one anyway.
Restore the power and check your work - the light should go on and off as you operate the switch.
Now work on the second light.
Good luck...Take care...
Peccavi
March 2009