function Londres() {
 today = new Date();
 opening = new Date(2012, 6, 27); // months start at 0 => 27/07/2012
 msPerDay = 24 * 60 * 60 * 1000 ; // Number of milliseconds per day
 msTimeZonediff = (today.getTimezoneOffset()+120)*60*1000; //Time difference
 daysLeft = (opening.getTime() - today.getTime() + msTimeZonediff) / msPerDay;
 daysLeft = Math.ceil(daysLeft);
   if(daysLeft >=0) {
 	    document.write(daysLeft)
   }
}
Londres();