I don't know why it didn't occur to me sooner, but when I started saving our margarine containers for other uses, I suddenly realised how many we were going through. When my plastics cupboard refused to take any more, I began**shock horror**throwing them in the bin again. I knew there had to be a better way!
Ironically, we've always used block butter for our cooking, so it wasn't hard to simply buy extra blocks to use as spread. We continually use the hard plastic container (in the above image) which we simply place the butter block into - and the best part is, the only rubbish which goes in the bin is paper.
A very simple stratagy I'm surprised I didn't key into sooner.
For easy spreading, I keep the plastic container in the pantry where it's cooler and it's right next to the spreads too. So I'm not opening the fridge every time I want to make a sandwich. In summer, with the heat, that's a good thing! It means less energy consumption too.