$.ajax({
    type: 'POST',
    url: "http://data.niassembly.gov.uk/organisations.asmx/GetPartiesListCurrent_JSON",
    contentType: 'application/json; charset=utf-8',
    data: JSON.stringify({}),
    dataType: 'json',
    success: function(data){
        if (data.hasOwnProperty('d')){
            msg = data.d;
            } else {
            msg = data;
            }
            alert(msg);
    }
    ,
    error:function(){
        alert('error');
        }
});