Private dogs are subject to the Dangerous Dogs Act; http://www.opsi.gov.uk/ACTS/acts1991/ukpga_19910065_en_1 That covers out of control dogs and dogs belonging to 'banned breeds'.. In the circumstances we're talking about, a successful prosecution against you for your dog biting a burglar or a mugger is extremelly unlikely. In fact, in over 12 years of law enforcement, I can't remember any one such occasion. More often than not, the family pooch stands by and watches whilst the lady of the house is raped and murdered. Although my dog is a 'family member' and a pet, she's also a personal protection dog. I'd rather she gave her life, than me, my wife or kids. Harsh, but fair and honest.