use strict;

sub flush_address {
  # may need more code to narrow down the address
  print "FOUND:\n>> ", join(">> ", @{$_[0]}), "======\n";
}

my @address;

my $line_span = -1; # -1 disabled; otherwise extract $line_span lines

while (<>) {
   # identify start of an address section (upd.: regexp incomplete)
   push(@address,$_), next if /^\s*(Miss|Mister|Mr\.?|Ms\.?|Her|His)\s/;
   if (@address) {
        push @address, $_;
        # identify end of an address section
        # regexp matches empty line here but should match something 
        # like "BN2 ..."
        if (@address == $line_span or /^\s*$/) {
          flush_address(\@address);
          @address = ();
        }
   }
}

flush_address(\@address) if @address;

__END__
pb> perl 733738.pl invoice.txt
FOUND:
>> Miss ***** ******
>> 1** Elm ****,
>> Bri*****
>> E*** ******
>> BN2 ***
>>
======