A retractor for a vehicle restraint system has a locking mechanism comprising an additional inertia member (7) which decouples from the webbing spool when a predetemined acceleration or deceleration force is exceeded, due to the pretensioning operation taking place, and operates a locking pawl (3) to prevent further movement of the spool. The locking pawl (3) is then positively held in the locking condition using a spring catch (9) integral with the inertia member (7), or it can be spring biased in the locking condition using a spring displacing the inertia member (7) against the locking pawl (3) once shear pins (8) have been destroyed. This prevents webbing payout in a multiple crash situation, and provides a positive indication that the pretensioner has fired.