toLocaleDateString() formatting

Question

I am using the above method to format my date, but for some reason it is formatting the date using the English US format: MM/dd/YYYY even though the locale for my site is English United Kingdom.

I tried the following variation: toLocaleDateString('en-GB') but it is still not working either. Any ideas?

Here is a copy of my code:

(function () {
    var statusFieldCtx = {};

    statusFieldCtx.Templates = {};
    statusFieldCtx.Templates.Fields = {
        "MaxEndDate": {
            "View": ColorCodeDueDate
            }
    };

    SPClientTemplates.TemplateManager.RegisterTemplateOverrides(statusFieldCtx);
})();

function ColorCodeDueDate(ctx) {
    var dueDate = new Date(ctx.CurrentItem.MaxEndDate);

    var now = new Date();
    var then = new Date();
    then.setDate(now.getDate() + 180);

    // if there's no due date don't render anything
    if (dueDate == 'undefined' || !dueDate) {
        return '';
    }
    else if (dueDate >=now && dueDate <= then) { // we are within 180 days
        return "<div style='background-color:red;color:white'>" + dueDate.toLocaleDateString('en-GB') + "</div>";
    }
    else {  // we are outside of 180 days
        return "<div>" + dueDate.toLocaleDateString('en-GB') + "</div>";
    }
}