Quick answer
Brown is live, blue is neutral, green/yellow is earth. In older UK wiring, red is live, black is neutral. Do not work on wiring without switching off the circuit.
UK electrical cable colours changed in 2004 to match European standards. In new wiring: brown is live (the dangerous one), blue is neutral, and green/yellow striped is earth. In older houses (wired before 2004), you may see: red for live, black for neutral, and green or bare copper for earth. If your home has old wiring, it is safe as long as it is in good condition — the colours do not need to change, but the wiring should be assessed by an electrician as part of an EICR. Never touch any wires without first switching off the circuit at the consumer unit and confirming the circuit is dead with a voltage tester.
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