Quote 1:
"Local Councils, animal health officers and the police have the power to enforce the law. If you suspect somebody is a puppy farmer report them to the RSPCA, the police, or your Local Authority"
Source:
http://www.thekennelclub.org.uk/our-resources/kennel-club-campaigns/puppy-farming/how-to-help-stop-puppy-farming/
Quote 2:
"Prospective buyers who suspect they are meeting a puppy farmer or agent should never agree to purchase the puppy – this simply fuels the trade, causing even more puppies and breeding bitches to suffer.
Instead they should report the incident to their local authority or Consumer Direct on 08454 04 05 06.
If you suspect that a breeder is a puppy farmer, contact your local authority, who will be able to investigate"
Source:
http://www.pupaid.org/puppy-farming/what-to-do-if-you-have-suspicions-about-a-puppy-farmer.html
So perhaps the Trading Standards department of your local authority could help?
However don't give upon the RSPCA. They were quick enough to respond (and to take my cat away) when someone reported me for 'neglect'. (The cat was actually very old and nearing the end of his life. The vet had said that he wasn't suffering and that, despite looking very poorly, he'd still enjoy exploring his territory and generally being made a fuss of until he could die naturally, rather than being put down unnecessarily. Once the RSPCA had spoken to the vet, they returned my cat and he passed away a few weeks later, curled up on my knee).