ConceptScheme as a subset of another?

Hello

I'm getting my head around SKOS with a view to seeing how well we can
represent UK public sector vocabularies hosted by esd.org.uk in SKOS and
derive online viewers and other human and machine readable resources from
the RDF.

My initial question relates to whether or not SKOS supports what esd knows
as "subsets".  For example these two online viewers:

   - Subject vocabulary: http://www.esd.org.uk/standards/ipsv/viewer/
   - Service vocabulary: http://www.esd.org.uk/standards/lgsl/viewer/

both feature drop down lists towards the top left of the page.  From the
drop-down list you can select a named "subset" which contains some of the
concepts from the main list (eg you can limit UK local government services
to those delivered in Scotland).

I understand that the skos:inScheme property can be used to say a concept is
in a particular ConceptScheme and this can be used many times to say the
same concept is in many schemes.  I can't say that one ConceptScheme is in
another can I?

Is there any sensible way I can support these subsets?

Thanks in advance
Mike