What is the process for reporting a DDoS attack to UK authorities?

To report a DDoS attack in the UK, individuals and businesses should primarily contact Action Fraud, the UK's national reporting centre for fraud and cyber crime. They can be reached online or by phone. For more serious incidents affecting critical national infrastructure or significant UK organisations, the National Cyber Security Centre (NCSC) should also be informed. In immediate emergencies or if there's a direct threat to life, contacting the local police is appropriate.