@Keypad well worth looking on ucas.com, for the course he's interested in at Durham, at the new Entry grades data section, which gives metrics for:
-Ratio of offers to applications
-Grades of current students on course - highest, typical and lowest
which may provide more confidence, or not, regarding how he would fit into the "grades demographic" for the course.
One aspect to be aware of is how popular the course is for international applicants - there are separate metrics available on their website providing the breakdown of international vs UK applications/offers per course.
My DS had Durham as his #1 choice when he was applying, with predictions of A*, A , A for an AAB typical offer course, but was rejected. Conversely, some of his friends with predictions of the typical offer for their courses did receive offers.
It's a fantastic university (I'm a Dunelm graduate, albeit a long-in-the tooth one) so if he really wants to go there and has predicted grades meeting the typical offer, I'd say go for it.