Are you sure the black that is taped off is not a red indentification tag.
The reds should be together as you have stated
The earths should be not wound together but terminated in to either an earth terminal on your light fitting or a seperate one for there use only and sleaved with green and yellow pvc sleaving, go buy some!
Now the two blacks should go to blue flex side of light fitting and the one with the tape on should be terminated at the brown flex side. if i'm right about it being the switch live and that should do the trick.
Remember to isolate circuit before you do this.
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