Erk!
```python
>>> fname = '/data/local/dataZoo/PP/COLPEX/small_colpex_theta_p_alt.pp'
>>> cube = iris.load_cube(fname, 'air_potential_temperature')
>>> print cube
air_potential_temperature / (K)     (time: 6; model_level_number: 10; grid_latitude: 83; grid_longitude: 83)
     Dimension coordinates:
          time                           x                      -                  -                   -
          model_level_number             -                      x                  -                   -
          grid_latitude                  -                      -                  x                   -
          grid_longitude                 -                      -                  -                   x
     Auxiliary coordinates:
          forecast_period                x                      -                  -                   -
          level_height                   -                      x                  -                   -
          sigma                          -                      x                  -                   -
          surface_altitude               -                      -                  x                   x
     Derived coordinates:
          altitude                       -                      x                  x                   x
     Scalar coordinates:
          forecast_reference_time: 2009-09-09 22:00:00
     Attributes:
          STASH: m01s00i004
          source: Data from Met Office Unified Model 7.04
>>> cube.remove_coord('model_level_number')
>>> print cube
air_potential_temperature / (K)     (time: 6; -- : 10; grid_latitude: 83; grid_longitude: 83)
     Dimension coordinates:
          time                           x       -                  -                   -
          grid_latitude                  -       -                  x                   -
          grid_longitude                 -       -                  -                   x
     Auxiliary coordinates:
          forecast_period                x       -                  -                   -
          level_height                   -       x                  -                   -
          sigma                          -       x                  -                   -
          surface_altitude               -       -                  x                   x
     Derived coordinates:
          altitude                       -       x                  x                   x
     Scalar coordinates:
          forecast_reference_time: 2009-09-09 22:00:00
     Attributes:
          STASH: m01s00i004
          source: Data from Met Office Unified Model 7.04
>>> iris.save(cube, 'wibble.pp')
Failed to get value ('NoneType' object has no attribute 'points') to execute:     pp.lblev = scalar_coord(cm, 'model_level_number').points[0]
Failed to get value ('NoneType' object has no attribute 'points') to execute:     pp.lblev = scalar_coord(cm, 'model_level_number').points[0]
Failed to get value ('NoneType' object has no attribute 'points') to execute:     pp.lblev = scalar_coord(cm, 'model_level_number').points[0]
Failed to get value ('NoneType' object has no attribute 'points') to execute:     pp.lblev = scalar_coord(cm, 'model_level_number').points[0]
Failed to get value ('NoneType' object has no attribute 'points') to execute:     pp.lblev = scalar_coord(cm, 'model_level_number').points[0]
Failed to get value ('NoneType' object has no attribute 'points') to execute:     pp.lblev = scalar_coord(cm, 'model_level_number').points[0]
...
```