Found the answer (for my problem, anyway) here:
http://www.perldoc.com/perl5.8.0/pod/perluniintro.html#Displaying-Unicode-As-Text
and adapted it to solve my need thus:

sub hexent {
    my $utf8=shift;
    # convert utf8 characters greater than 255 into hex entities
    my $mapped=join("", map { $_ > 255 ? sprintf("&#x%04X;", $_) : chr
+($_) } unpack("U*", $utf8));;
    return $mapped;
}
[download]

Four of hardest-to-understand Perl function in one command line!

Hope this helps you with your problem ...

AndyH