Hi Jamie
Firstly SWITCH OFF AT THE FUSEBOARD the circuit that controls this before you do anything.!
The two cables that contain a black and a red are feeds to and from the ceiling rose. Those two reds should be connected to each other, and to one of the red wires in the two red (switchwire) and then sealed off.
The two blacks should be connected together and are the neutral connection for your new light. (connect to the blue N terminal/wire on your light)
The one remaining red wire (the other one from the pair of reds switch wire) is your live collection for your new light. Connect this to your brown L terminal/wire on your new light.
All three earth wires (probably bare, or sleeved with green/yellow) should be connected together, and connected to the ground E terminal/wire on your new light.
If you are wiring up a new plastic ceiling pendant there is a strip of connectors running across the backplate. If you look carefully t is divided up into sections. The three red wires all go into the central strip of three terminals, the two blacks go into the other set of three terminals next to it. The lone red goes into the double terminal to the other side of them. The earth wires all go into the lone separate terminal/connector off to the side.
I hope this helps, and is not too confusing. Also please bear in mind that I am making some (normally correct) assumptions, and without seeing it in person it can never possible to be to know that someone hasn’t previously done something “unusual”.
StMark
March 2011