Seat belt inertia reel not locking - Pass & advise or Fail ?

Only available RfR for Retracting Mechanism is the one below nt

5.2 Seat Belt Condition, b. a retracting mechanism does not retract the webbing sufficiently to remove all the slack from the belt with the locking mechanism fastened and the seat unoccupied.

Here you go

If an inertia reel seat belt doesn’t ‘lock’ when pulled, this is a Reason for Rejection (RfR).

There is no requirement to assess whether an inertia reel belt ‘locks’ when you tug on it. However, we know that some testers have used RfR 5 in Section 5.2 for this (“The locking mechanism of a seat belt does not secure or release as intended”) even though this is only meant for the seat belt buckle mechanism.

mattersoftesting.blog.gov.uk/urban-myths-of-the-mot-test/

Ya thats a myth Gaz
What the blog is saying is testers have been getting it wrong

Does that test airbags as well?

P&A for sure. The RfR I posted above is the only one available and it doesn't cover the inertia reel. The inertia operation isn't part of the test..