Or to reuse the same 'soap' prefix do:

<xsl:attribute name="{$q}"
namespace="{namespace-uri-for-prefix(prefix-from-QName($q), .)}">

<fault>
<xsl:attribute name="{.}"
namespace="{namespace-uri-for-prefix(prefix-from-QName(resolve-QName(.,.)),.)}">blah</xsl:attribute>
<xsl:value-of select="."/>
</fault>

________________________________________________________________________
The Numerical Algorithms Group Ltd is a company registered in England
and Wales with company number 1249803. The registered office is:
Wilkinson House, Jordan Hill Road, Oxford OX2 8DR, United Kingdom.