In order to do this, you have to choose a time zone.
I assume you mean "London":

use DateTime::Format::ISO8601;
my $parser = DateTime::Format::ISO8601->new();
my $dt = $parser->parse_datetime( '2004-10-05' );
$dt->set_time_zone( 'Europe/London' );
print( $dt->is_dst ? 'Y' : 'N' )
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