https://www.askthe.police.uk/content/Q524.htm
Amendments to the Dangerous Dogs Act mean it is now an offence for a dog to be dangerously out of control in a public place and on private property.
Though intruders into your home would generally not be covered by the amendments, all the circumstances will have to be considered and each decision will be judged individually. For example if you deliberately set your dog onto the intruder and they then suffer injury, you may be liable for prosecution and the dog ordered to be kept under control.
However, if you are not home and your dog attacks, it is unlikely that you would be liable for the attack. This defence only applies in your home and not other premises or land i.e. if a person (intruder of otherwise) enters your garden and is bitten by your dog, you may be liable.