To me this sounds like the whole nonsense surrounding child protection/CRB checks and how routinely, males (whether they be your partner, or your partners parents, where they are most probably only really interested in your partners father, although social workers would not dare openly proclaim that stance) are automatically by social workers presumed to be guilty/present-a-potential-danger to ALL children. It is only when CRB checks say they are not, that social workers will finally (and reluctantly in a lot of instances) and begrudgingly curtail their behind closed-door fingerpointing/gossiping.
Your other potential problem could be CRB itself. As first conceived and instigated it was clear and unambiguous. It simply reported 'criminal' records. You mentioned CRB, although I suspect it is 'enhanced CRB' checks they are referring to. What social services should be checking for is: (a) criminal record per se (although why many possible criminal records have the slightest bearing on parenting etc is beyond me and most other people!) and (b) checks of sex-offenders registers etc (now all at the ISA). OK, there is nothing irrational about having these checks performed.
What can throw 'spanners' into the works are the 'enhanced' revelations in an 'enhanced CRB check'. These are purely at the whim of the chief constable of the local force and in effect allow the police simply to regurgitate anything they have recorded in local police files. You can be of the view that Police are very sensible and record in their files sensible statements, but my own experience and knowledge of what has happened to many other parents, is that is not the case. Anyone, anyone at all can, anyone that has a grudge against you, or any other person, can call the police and make any number of allegations/statements about any person they like. These, without any proof, and equally without any serious and proper investigation, will undoubtedly turn up in an 'enhanced CRB' disclosure. Such disclosures are so open to abuse and to being easily manipulated, that to any sensible person they have no credibility, yet social services (and many other 'quango' bodies) believe every word of them.
So, those are some the dangers you may face in your move to adopt. In terms of what the guidance is for running CBR checks, I do not believe there is any what so ever. How you understand where social services is going/what their intentions are is often very difficult to establish...in large part they often appear to be 'making it up' as they go along. I would suggest you read and re-read everything you can find online about them and their procedures (this will most probably be somewhere within the councils web site, that the social services/CYPS are part of). If you cannot find precise statements (..and I doubt whether you will, their words are often a mixture of politically correct statements/supposed intentions), then I would formally write to them and asked specifically for a copy of their Policies and the Procedures, inclusive of the Operating ones (i.e. not simply the good words at to what they ought to be doing, but how it is being done, e.g. social worker A, reports to B, C oversees, D makes the final decision(s) etc etc) themselves that relate to Adoption. State also, how you have not so far managed to locate any Procedure(s) that relate to CRB checks and make sure you also them to include their method of working in this respect where it is not covered in any of the other Procedures. This is to stop them simply giving you a lot of Procedures, which have no, or little mention of CRB.
Equally, you may find their Procedures or statements of what they are supposed to be doing, in effect 'fob' you off, via wholesale reference to things like the 'Every Child Matters' framework. If they do, keep pushing, by asking them for precise details as to how they implement (..on a day to day basis) those parts that are relevant to Adoption. For example, whatever social workers are doing, they are most certainly filling in computer based forms, with check boxes and they like, they are working through. Indeed ask them for a copy of those screens/forms (don't have to contain any sensitive info, just copies of the blank screen) as that advise you of what is driving their actions.
Hope this helps, sorry if it is not too encouraging, but my own experience with social workers (albeit not related to Adoption) is that you have to keep pursuing them from all corners to get the information you are after.