For one thing, you can do something like:

my @records = <BIGFILE>;
[download]

which will slurp but does not chomp at the same time; however, the impact of the CR will have little effect on your matching.

Since you then have to write out to a file, there's no need to wastefully add the carriage return before you split the file, so instead, you can do:

my @records = <BIGFILE>;
my @london = grep /LONDON/, @records;
print LONDONFILE join "", @london;
[download]

Finally, this type of situation is an ideal one where slurping is inefficient, unless you're repeating the process multiple times; it's probably much easier and less of a memory hog to process line by line:

while ( my $line = <BIGFILE> ) {
   /LONDON/ ? print LONDONFILE $line,"\n" : 
              print OTHERFILE  $line,"\n";
}
[download]

Updates as arturo pointed out to me that slurping in array mode doesn't chomp.

-----------------------------------------------------
Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
It's not what you know, but knowing how to find it if you don't know that's important