The change forward is not a problem, it's moving back that creates the ambiguity. As I see it you need to delay applying the UTC timezone until the second sequence of 01:00 to 01:59 times on the change day. I suggest using the is_DST method to detect the change, and a hash to remember when the time repeats. For example : 

#!perl
use DateTime;
use DateTime::TimeZone;
use strict;
my %seen=();
my $tz = 'UTC';
my $last;
while (<DATA>){
  chomp;
  next unless ($_);
  my ($y,$m,$d,$hr,$min) = split /\D/,$_;
  print "$_ : ";
  my $dt = DateTime->new (
    year   => $y, month  => $m,
    day    => $d, hour   => $hr,
    minute => $min,    
    time_zone => 'Europe/London',
  );
  
  print $dt->is_dst," : ";
  if ($m==10 && $hr==1){
    if ($dt->is_dst() ne $last){
      $tz = '-1:00';
    }
    $tz = 'UTC' if ++$seen{$min} > 1;
  } else {
    %seen=();
  }

  $last = $dt->is_dst();
  $dt->set_time_zone($tz);   
  print $dt->strftime("%Y-%m-%d %H:%M"),"  $tz \n";
}

__DATA__
2014-03-30 00:59
2014-03-30 02:00
2014-03-30 02:01
2014-03-30 02:30
2014-03-30 02:59
2014-03-30 03:00
2014-03-30 03:01
2014-03-30 03:30
2014-03-30 03:59
2014-03-30 04:00
2014-03-30 04:01
2014-03-30 04:02

2014-10-26 00:59
2014-10-26 01:00
2014-10-26 01:01
2014-10-26 01:30
2014-10-26 01:59
2014-10-26 01:00
2014-10-26 01:01
2014-10-26 01:30
2014-10-26 01:59
2014-10-26 02:00
2014-10-26 02:01
2014-10-26 02:02

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In reply to Re^8: Converting local time to utc time by poj
in thread Converting local time to utc time by ureco

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