An Arc-fault Circuit Interrupter (AFCI) or Arc-fault Detection Device (AFDD) is a circuit protective device designed to protect against fire caused by arcing - an RCD might not detect arcing.
Soon, the UK Wiring Regulations (18th edition) may include protection by AFCI/AFDD.
- RCD in UK DIY Wiki
- Wikipedia - Arc-fault Circuit Interrupter
- Search UK Web for AFCI
- IET : BS 7671: the 18th Edition report, in "Wiring Matters"