Please advise on animal cruelty (read on)...?

If you cannot make an anonymous report, the RSPCA should be able to keep your identity private. All they need is reason to visit the facility - they don't need to divulge info about who made the report. If it makes you feel better, talk to them about this before providing the information. If these are primates, then it is my understanding that they are being illegally kept - I'm not from the UK but I know their animal cruelty laws are generally stricter than those in North America. Good luck.