One of the earlier versions of ZZPS called Roxburghe (UK) (see fit and proper persons) used GPB Solicitors to send out dummy Letters before Claim. This format is being recycled for use by other companies even today. You'll notice that it claims that the debt collector in this case, Roxburghe, can instruct the solicitors to issue a claim. This is of course false as only the principal can do this.
Sadly GPB are no more (see suspected dishonesty). Working with these debt collectors can have a serious effect on legal firms and solicitors as others have found out.