Hi Rob,
The immediate check on whether its is charging is the ign warning light in the speedo (normally the red one). It should go out as soon as the engine revs up a bit and only come on flickering a bit at tickover. If the light does not come on when first switched on then the bulb has probably blown. In which case the dynamo will not work as it needs the current provided through the bulb to to get the dynamo started.
If thi is the problem, then the neutral light bulb or the speedo light bulbs are all the same dimensions and could be used as a stop gap.
Peter