gistfile1.txt

// From http://stackoverflow.com/questions/3583989/jquery-autocomplete-pass-targeted-element-attribute-as-an-extra-parameter 

$("#autocomplete input").each(function() {
   var that = this;
   $(that).autocomplete({
        source: function(request, response) {
            $.ajax({
                url: "search.php",
                dataType: "json",
                data: {
                    term: extractLast(request.term),
                    extra_param: $(that).attr('id')
                },
                success: function(data) {
                    response($.map(data, function(item) {
                        return {
                            label: item.label,
                            value: item.name
                        }
                    }))
                }
            })
        },

    });

});

Theres probably more scope to make it more efficient, but breaking it into an each first allows you to set 'that'

Yay! That's worked - cheers mate :)