Hi Charles

Last autumn/winter I decided to go over to your system of 'no dig',
having a great dislike to the usual double digging. Today I really
enjoyed planting my early potatoes in the soft soil that the horse
manure I used has created. I have to admit though that I'm not quite
sure how putting more manure or compost over the top will allow the potatoes to grow?
I obviously have a little while to decide how I am going to proceed.

Thanks Ruth

 It sounds a great start Ruth. 
Think of potatoes rooting in two different ways. Plants send roots into soil below and around (dug or undug) for moisture and food, at the same time as their new tubers swell near the surface. Tubers are a fodd store, next year's growth, and they swell nicely in surface compost, manure and mulch. How much you need depends on how long the plant grows for (so First Earlies less) and how big they become. Tubers also need protecting from light and any organic matter on top can achieve this (card, mowings of grass, straw) or black plastic.

The essence of it is that potato tubers swell beautifully in surface organic matter, and come out clean.

By charles