Thanks to all who have read this post, scratched their heads and moved on ... I've now found a partial answer on a FME forum at Safe Software. It seems that the way OS structure their GML means that transformers are not able to gather these data, so it is necessary to program a solution using the FME API. As I'm not aware of having access to this API through ArcGIS, I think I'll go and program this up independently. Best wishes, Peter
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