Hi Longshaw,

Two different issues here.

First off the tiny white worms in your compost are likely to be Enchytraeids (AKA Potworms). These are digester's of waste plant material, much like earthworms, and don't require "treatment" at all. Having said that, they generally only thrive when conditions are damp or even water-logged (conditions that don't suit earthworms) so this would suggest that your compost is too wet.

In terms of the blackfly I'll adapt an answer I gave to someone else....on an edible plant like Basil you obviously don't want to use anything toxic, and in fact you don't need to. One easy option is to use washing-up liquid and water as a spray which effectively suffocates the aphids. However you must use a vegetable based soap (like Ecover) or you can do all kinds of damage to both the plant and the soil. This has no long-term/residual effect though so you do need to spray pretty regularly to prevent re-infestation and maintain control.

Slightly longer lasting are a variety of "home brew" plant based sprays. There's some info about some of these in this article at Ecocharlie:

http://www.ecocharlie.co.uk/blog/index.php/2010/03/08/plant-pests-%E2%80%93-ten-top-organic-solutions

The garlic & chilli sprays definitely work very well - I've used them successfully on aphids, sawfly & caterpillars, and I like the idea of using the defences of one plant to help protect another. They will kill aphids on contact and will also leave at least some residue that will deter new aphids from setting up home

Great info Ilex... we've been using a commercial garlic spray will make our own in future!