Vicky, while UK NARIC writes the database, the database doesn't consider certain things which a NARIC letter would. You have to provide both your degree and your transcripts for a NARIC letter. It is very conceivable that database, being very black and white would be an different result then a manual process that looks at degree and the transcript.
In my spare time, I am trying to get some sort of official stuff rolling (as you may have noted from my posting in Advocacy), but for now, the best bet is to get the NARIC Letter if there is doubt about if the degree is equivilant. If there is any doubt someone can spend the £65 and be sure. How can someone disagree with the database until they have the NARIC Letter anyways?