Thales007 - Thank you for your input, unfortunately your solution would not work in this case. The information in each polygon (and therefore point) is amended on a weekly, sometimes daily basis. Converting it to raster would just mean more work.
jborgion - I have used a spatial join in the past but it creates a new feature which is not ideal (see above). However, I have given it some thought, and while I am no expert, I feel using modelbuilder to create a workflow would help speed things up. Tell me what you think:
Manually enter delivery information then - Dissolve feature based on delivery number > spatial join (SJ) polygons to points > Select points by location within dissolve feature (to speed things up) > join SJ feature to points based on postcode > field calculator data into relevant fields > Remove join > delete SJ feature.
I'm not even sure model builder can do that but I would like to think it can.