Many thanks for the feedback guys, I'd really appreciate some help with this - the script works fine apart from the closed filehandle error. As mentioned before, I'm assigning the current session name as the filehandle for printing, which I thought would be unique but I might have misunderstood the POE code. Here it is:

#!/usr/bin/perl
use warnings;
use utf8;
#use strict;
use LWP::UserAgent;
use HTTP::Request::Common qw(GET POST);
use POE qw(Component::Client::HTTP);

#capture the search term
print "Welcome, please enter your search term: \n";
chomp (my $term = <>);
my @url_list=();
if ($term){
    my $browser = LWP::UserAgent->new;
    $browser->agent('Mozilla/6.0');

#post the search query to Scroogle
my $response = $browser->post(
'http://www.scroogle.org/cgi-bin/nbbw.cgi',
['Gw'=>$term, 'n'=>'1', 'l'=>'en']); # set the volume and language of 
+the returned pages

#build a list of returned links
if($response->is_success){
$response = $response->decoded_content;
@url_list = ($response =~ / href="(http:.*?)"/g);
%urls=();
my $count =1;
foreach (@url_list){
$urls{ $_ } = $count;
$count++;
}
}
}

#Setup the virtual browser and its configuration
POE::Component::Client::HTTP->spawn(
  Alias   => 'Mozilla', #alias of the url request to the web server
  MaxSize => 300000,    # Set the maximum HTML page size you want to r
+etrieve.
  Timeout => 20,    #this is the number of seconds to wait before canc
+elling retrieval
);

# Create a session for every URL taken from the search.
foreach my $url (@url_list) {
  POE::Session->create(
    inline_states => {
      _start => sub {
        my ($kernel, $heap) = @_[KERNEL, HEAP];

        # Post a request to the HTTP user agent component.  When the
        # component has an answer (positive or negative), it will
        # send back a "got_response" event with an HTTP::Response
        # object.
        $kernel->post(Mozilla => request => got_response => GET $url )
+;
      },

      # A response has arrived.  Display it.
      got_response => sub {
      my $id = $_[SESSION]->ID;
        my $filehandle = $id;
        
        my ($heap, $request_packet, $response_packet) = @_[HEAP, ARG0,
+ ARG1];

        # The original HTTP::Request object.  If several requests
        # were made, this can help match the response back to its
        # request.
        my $http_request = $request_packet->[0];

        # The HTTP::Response object.
        my $http_response = $response_packet->[0];

        # Make the response presentable, and display it.
        my $response_string = $http_response->decoded_content();
        $response_string=~ s/[[:^ascii:]]/ /g; #removes non ASCII char
+acters
        $response_string =~ /<title>(.*?)</; #captures the webpage tit
+le
        my $rank = $urls{$url};
        if ($1){
        my $title = $1;
        $response_string =~ s/<(?:[^>'"]*|(['"]).*?\1)*>//gs; #removes
+ the HTML
        #$response_string =~s/[^a-zA-Z]|\D|[^\.'\-\$]/ /g; #replaces n
+on character text with whitespace
        my @paragraphs = split /\n/, $response_string; #this splits up
+ every paragraph in the remaining text
        my @results;
        foreach (@paragraphs){
        if (/ $term /){
        unshift(@results, $_); 
        }
        }
        if (@results){
        print "Content for $term found at $url\n";
        open ($filehandle,">>:utf8", "c:/perl/results/$title.txt"); #c
+reates a new file
        print $filehandle "$url\n$rank\n"; #prints URL and  search eng
+ine ranking to the file
        foreach (@results){
        print $filehandle "$_\n";
        }
        close $filehandle;
        }
        else{
        print "No relevant text found at $url\n";
        }
        }      
      },
    },
  );
}

# Run everything, and exit when it's all done.
$poe_kernel->run();
exit 0;
[download]

I changed the scalar used for the filehandle to a unique global array element ($rank), and changed the to-be created filename to a simpler scalar ($rank . $term). This fixed the issue and now it works great...except scroogle went down today :( .