I undertook a trial a few weeks ago for a couple who had been prosecuted by the RSPCA for causing suffering to a cat. The cat had developed a tumor which had caused an abscess. The vet said that the couple would have known that the cat was in pain. This couple looked after many cats. They loved animals. They cared for animals. The Magistrates did not convict them and teh couple walked free from Court after trial.
Two issues arise:
1 The RSPCA is a charity. They are not the Police. They do not have the right to enter your home or property unless you invite them. You don’t have to let them in-unless accompanied by a Police Officer.
2 You don’t have to answer their questions. They may give you a caution before interviewing you, but you don’t have to speak to them if you don’t wish to. Apart from that you might wish to take legal advice before the interview or have a solicitor present during interview.