I don't really like soil, but I use a nice soil-like substrate.

1/2 Sphagnum Peat Moss (I don't know where you might be able to find peat moss in Scotland Ooh, I could use a nice glass of single-malt highland whiskey right now, something with a speyside fruitiness)

1/2 Pearlite

A good fistfull of dolemetic lime. (It has a neutral PH and helps buffer the PH)
Worm castings or compost can be added to give it nutrients at seedling levels, since it won't have the built-in nutrients of soil.

No chemical ferts for seedlings!!!

This mix makes it hard to over-water, roots love it, and I never get bugs in it like I did when I was using potting soil. Saving money on diatomaceous earth.