Sometimes, a mortgage application goes wrong; when it does, you should always be able to understand what caused it to go wrong.  A lender should be able to give some information; however, in this case, they seemed unwilling.

Hi, I recently applied for a mortgage; everything was going well until, out of the blue, I got an email from the lender stating my application was being declined.  No reason was given, so I called them.  They told me it was due to the credit search.  I did try to probe, but they told me nothing at all.  I have searched Equifax and Experian; both show excellent scores. Experian has me at 999.  Can the lender refuse to tell me anything?  If I go to another lender, the same might happen, so I must fix whatever they see.

When lenders decline an application, they should provide two pieces of information.  The first they have provided is the reason for the decline, in this case, a credit search.  The second piece of information is the agency's name that provided the information that led to the decision.  They can't refuse to provide that information.

I suggest getting in touch and explicitly asking for the name of the agency they used.  Some lenders use more than one, simply as different agencies can contain different information.  You have already checked two main three that leaves Call Credit.  As well as contacting the lender again, run a report at Call Credit now known as Transunion to see if anything shows up.  ClearScore is another one to check.  Lenders don't use them, but they're another source of information about your credit file, albeit provided by Experian.

If not, push the lender for a name.  If they refuse, then complain.  I am hoping that it's simply a misunderstanding as I find it very strange they are unwilling to provide the agency's name.   Lenders are well aware that you need that information to investigate further.

You're right in that you need to know.  If two reports show nothing and return a high score, then it is necessary to establish what they have found, or it could happen again at another lender.

They are not obligated to tell you what they found or how it impacted your application.

Good luck, and let me know how you get on.