I haven't had any similar experiences Anna but personally i'd be preparing a policy for inclusion within your emerging Local Plan rather than relying on a saved policy from what I assume is a rapidly ageing Structure Plan. Whilst the purposes of including land within the Green Belt hasn't changed across PPG3-PPS3-NPPF, it's logical to bring the direct control/management of your small area of Green Belt within that of a Local Plan and ensure that it falls in line with all other policies you may be producing at the moment.
Much depends though on how Structure Plans are still viewed by Inspectors and the weight they are given in decision-making. I fear you may well face a situation where if pressures unexpectedly arise in your area of Green Belt, you are left without anything robust enough to fight inappropriate development. Developers are bound to argue that the GB was designated through the Structure Plan process decades ago and hasn't been assessed alongside all the other newer NPPF-compliant policies your local authority is in the course of producing.
Whilst it may add to your workload (sorry!), a quick but transparent review to help reaffirm the GB's current extent and enable you to produce a policy (reflected on your Policies Map) would be appropriate if you were still in the earlier stages of plan-production.
