The RSPCA Injustic blog reports a parliamentary answer which clarifies the legal position. Fact is, the RSPCA have no right to seize pets.
Lord Elton: To ask Her Majesty's Government under what authority, controls and supervision and in what circumstances officers of a charity are empowered to (a) remove a pet from its owner's care, (b) keep it in their own care, (c) deny access to it to the owner, and (d) refuse to inform the owner of the place in which it is kept. [HL2038]
The Parliamentary Under-Secretary of State, Department for Environment, Food and Rural Affairs (Lord Davies of Oldham): Charities have no power under the Animal Welfare Act 2006 to seize pet animals. The power of seizure can be exercised only by a police officer, an officer of a local authority or Animal Health. If the person who was responsible for the animal has concerns regarding its welfare following seizure then it is open to him to apply to the court for an order which could, among other things, grant him custody over the animal. Anyone aggrieved by the removal of an animal under the Animal Welfare Act may appeal to a magistrate's court for its return. The location of a seized animal may be withheld if it is considered that there is a danger that the animal may be stolen back.
Read the entire post here.