sample.js

function onEdit(e) {
  
  new Date().toLocaleString("en-GB", {timeZone: "Europe/London"})
  var user = Session.getActiveUser().getEmail();
  var oldValue = e.oldValue
  var sName = e.source.getActiveSheet().getSheetName();

  if(sName == "Standards Assurance Table") {
    
    var mA1 = e.range.getA1Notation().split(":")[0];
    var timedate = new Date();
    var timestamp = Utilities.formatDate(timedate, 'Europe/London', 'yyyy-MM-dd HH:mm:ss Z');

    if(typeof(e.value) == 'string') {
      
      var aCell = e.source.getRange(mA1);
      var value = aCell.getValue();
      var form = "'" + aCell.getFormula();
      
    } else {   
      
      value = e.value;
    }

    var data = [timestamp, user, mA1, oldValue, value];
    e.source.getSheetByName("Change Log").appendRow(data);
    
  }
}