#!/usr/bin/perl -W
use strict;
use warnings 'all';
use Data::Dumper; $Data::Dumper::Useqq = 1; $| = 1;

my @field_names = qw(
  PROP
  COLOUR
  TXTCOL
  URL360
  USER
  YOUR_NAME
  ADDRESS
  TOWN
  ZIP_CODE
  COUNTRY
  EMAIL
  TELEPHONE_NO
  TELEPHONE_NO2
  THEME
  WEB_ADDRESS
  PPEMAIL
  JUNK1
  JUNK2
  JUNK3
);
# Simplified @field_names for this example:
@field_names = qw(
  PROP
  COLOUR
  USER
  YOUR_NAME
);

# 'Prop' is a unique key in file PAGE and in hash %onprop.
my %onprop; # HoH

# 'user' is not unique, so each hash entry will be an array of 'Prop's.
my %user_props; # HoA

while (<DATA>) {
  chomp;
  next unless /\S/;
  my @fields = split "\t";
  warn unless @fields == @field_names;
  my %h;
  @h{@field_names} = @fields;
  my $prop = $h{PROP} or warn;
  my $user = $h{USER} or warn;

  # Create array of users and hash of data
  warn "Overwriting '$prop'" if exists $onprop{$prop};
  $onprop{$prop} = \%h;

  push @{ $user_props{$user} }, $prop;
}
print Data::Dumper->Dump(
  [     \%onprop, \%user_props   ],
  [ qw(  *onprop   *user_props ) ],
);

print join("\t", @field_names), "\n\n";
foreach my $user ( sort keys %user_props ) {
  my @prop_list = @{ $user_props{$user} };
  my $number_of_props = @prop_list;
  print "Grouped data ($number_of_props lines) for user '$user'\n";
  foreach my $prop (@prop_list) {
    my %h = %{ $onprop{$prop} };
    my @fields = @h{@field_names};
    print join("\t", @fields), "\n";
  }
  print "\n";
}
__DATA__
foo	red	jonnyfolk	Saint J
bar	white	Util	Me
baz	blue	jonnyfolk	Saint J
qux	black	Util	Me2