An expected Lords' judgment may open the floodgates for animal attack claims. Philippa Craven explains

Man's best friend has a nasty streak. The Princess Royal has been convicted of charges brought under the Dangerous Dogs Act, her bull terrier having attacked two people in Windsor Great Park. In the US, Marjorie Knoller was convicted of murder when her dog killed her neighbour in a savage attack.

Recent statistics suggested a reduction in the number of dog biting incidents, but the the number of claims has risen. One pet insurer reported an increase in payouts from £375,000 in 1990 to £700,000 in 2000. In the US, insurers pay out $250m (£156m) over dog bite incidents and are looking at ways to limit liability under their policies.

Dog bite claims are dealt with primarily under the Animals Act [1971]. Lord Denning said that the Act was "very cumbrously worded and will give rise to several difficulties in the future". He was not wrong.

The Act sets out three tests which must be satisfied to establish liability. Section 2 (2) (a) is concerned with the type of damage that is foreseeable that an animal may cause. The damage must be of a kind that the animal, unless restrained, was likely to cause or, if caused, was likely to be severe. This section has not proved too difficult to interpret.

Section 2(2) (b) is the difficult test and deals with causation, stating that "the likelihood of the damage or of it being severe was due to characteristics of the animal that are not normally found in animals of the same species or are not normally so found except at particular times or in particular circumstances". This was considered in the case of Curtis v Betts [1990].

A claim for damages succeeded after a child was attacked by a bull mastiff as he climbed into the back of the dog owner's Land Rover. The dog had a known temporary characteristic of being ferocious when defending its territory - which included the car. The question of temporary and permanent characteristics was considered in the judgment by Lord Justice Stuart Smith.

An example of a permanent characteristic was held to be a dog with a known propensity to attack without reason; a bitch that attacked in defence of her litter did so while showing a temporary characteristic.

Section 2 (2) (c) deals with a keeper or owner's knowledge of an animal's characteristics. The situation has been changed by the Court of Appeal's judgment in Mirvahedy v Henley. This case involved horses that had escaped from a field, which was surrounded by an electrified fence, on to a road, causing a serious road traffic accident. The injured driver sued the owner of the horses under the Animals Act in negligence, and his claim at first instance failed.

The case was appealed. The Court of Appeal held that the accident had been caused by the particular characteristics of the horses, once they had been terrified into escaping, so it was because they were behaving unusually due to panic that the damage was caused. After bolting, the horses ran out on to the road and actually crashed into the cars causing damage and injury. The test under Section 2 (2) (b) was satisfied. The horses had temporary characteristics, but these were normal to the breed in certain circumstances and times.

It was enough that the defendants knew that horses could behave in the way that they did if frightened or panicked. In the past the owner would have to have known of the particular horse's tendency to bolt at a particular time or circumstance, compared to mere knowledge of the characteristic.

The defendants in Mirvahedy appealed to the House of Lords on 9 December. Judgment is expected in March. If the Court of Appeal decision stands, the floodgate for animal claims may be opened. The decision as it stands suggests owners need to exercise greater vigilance over their animals and insurers need to review their policies.

Philippa Craven is liability team leader at DLA Solicitors