There is no colour code, I was thrown off this forum in the past for trying to help work out wiring without use of a meter, so I don't want to do that again, I realise with the virus it is hard to find an electrician, so hope we can help, but need to first work out how you can test.
So cable A not a clue why three colours.
Cable C seems likely the cable to switch.
So maybe you can find other end of cable A in another ceiling rose, and this may help, I can guess the three cables are permanent line, switched line, and neutral, but not a clue which colour is which, best chance is finding other end in another ceiling rose, then you can copy like for like.
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