What about this:

print scalar localtime(), "\n";
$ENV{TZ}="Europe/London";
print scalar localtime(), "\n";
[download]

Prints the following for me (I'm in CET, that is Europe/Amsterdam):

Fri Sep 13 13:51:50 2002
Fri Sep 13 12:51:50 2002
[download]

Cheers,

Joe.