From the excellent book Digby Law's Pickle and Chutney Cookbook - well worth buying.
2 cups sugar
4 cups malt vinegar
3 cups strained cooking water
Scrub the beetroot very gently to remove all dirt. Cook in boiling water to cover for about 1 hour, until tender. Allow to cook, then peel and slice, reserving the cooking water.
In another saucepan combine the sugar, malt vinegar and cooking water, and bring to the boil. Add the sliced beetroot and bring back to the boil.
Pack the beetroot into hot, clean jars, cover with the hot liquid and seal.