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As far as I know, Wheat Starch is only available and allowable in the UK.  It
is specially processed here to meet with the International Standard for
gluten free foods (Codex Alimentarius).  It is used in a large variety and
selection of gluten free breads, biscuits, pasta, baking mixes, etc.  Having
moved to England from the USA (where I had never had anything made with wheat
starch), I must say that it makes a huge difference in the quality, texture
and taste of bread...making it nearly indistinguishable from gluten
containing bread.
For this reason, it is quite unfortunate that wheat starch is not used in the
USA although I understand that there are many people (in the USA) who feel it
is not truly free of gluten.  However, I must say that my daughter (the
Celiac) who adhered very strictly to a GF diet in the USA now eats it here
along with malt flavouring (another ingredient allowable by the UK Coeliac
Society) and oats and has not experienced one moment of illness.
Jane Oswaks, London