Nice one. I could not resist doing that in Text::CSV_XS' csv function (this won't fly if your file is huge):

use 5.20.0;
use warnings;

use Text::CSV_XS qw(csv);

my $n = 1;
open my $fh, "<", "file2.txt";
my %sort = map { chomp; $_ => $n++ } <$fh>;
close $fh;

csv (sep => ";", before_out => sub { shift @{$_[1]} }, quote_space => 
+0,
     in => [ sort { $a->[0] <=> $b->[0] } @{csv (sep => ";", in => *DA
+TA,
     after_parse => sub { unshift @{$_[1]}, $sort{$_[1][0]} // $n })}]
+,
     );


__END__
1 HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2305=27:2307=NAR@4;2306=en
+g@106:2308;2309=eng:0:21000:2:2066:0 
2 HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2315=27:2316=NAR@4;2317=en
+g@106:2318;2319=eng:0:21020:2:2066:0 
3 HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2320=27:2321=NAR@4;2322=en
+g@106:2323;2324=eng:0:21030:2:2066:0 
ITV HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2305=27:2307=NAR@4;2306=
+eng@106:2308

=>

3 HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2320=27:2321=NAR@4;2322=en
+g@106:2323;2324=eng:0:21030:2:2066:0
1 HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2305=27:2307=NAR@4;2306=en
+g@106:2308;2309=eng:0:21000:2:2066:0
2 HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2315=27:2316=NAR@4;2317=en
+g@106:2318;2319=eng:0:21020:2:2066:0
ITV HD;BSkyB:11097:VC23M5O25P0S1:S28.2E:23000:2305=27:2307=NAR@4;2306=
+eng@106:2308;2309=eng:0:21000:2:2066:0
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