1) terminate your two reds together with nothing else, one is your live supply from another fitting or cu, the other goes to the switch. Joining the two will supply power to switch
2) Your two blacks one is the neutral and the other is supplying a live via the switch this should have sleeving on or tag
3) Black with sleeving (switch wire) to brown flex side of light fitting, neutral black to blue flex side of light fitting (this configuration is especailly important with eddison screw lamps)
4) circuit protective conductors (aka earths, but this term is not true ) connected together and terminated to lamp earth terminal if ther is one especailly if metal fitting.
and let there be light
Kind regards stay safe and isolate prior to carrying this out.
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