local/less/mixins.less

Hi folks,
I am looking for a bit of insight please

I though I would create a new mixins.less file in the local folder (to test and learn the 'local folder' way of doing things) and it seems some files get compiled and some do not.

template.less and styles.less do

Mixins.less does not, even though there is a Mixins.less file in the less directory: [template_name]/less/mixins.less

I assume it is not compiling because it is not getting imported directly by the template.less file (though I expect I am completely wrong here).

Any pointers, tips, suggestions etc greatly appreciated.

Thanks in advance

Jon