Sounds like scale of some sort,possibly horse chestnut scale - these are brown sort of discs, usually with a white deposit around them - they later die and fall away, leaving behind white areas. If it sounds like this, then you need a spray for scale - Provado make one, but check that its suitable for use on food crops if you intend to harvest nuts. If you do want to harvest, then some time spent with methylated spirits and cotton buds (dab each one when they're present) and then cleaning off the deposits with insecticidal soap would probably be better.

Thanks Bamboo

I'm also guessing that this is a contorted Hazel and its growth habit is genetic and happens without training. The contorted type isn't as prolific bearing nuts as others but still produces the odd one here and there.