$(document).ready(function() {

    //check if box exists
    if ($("input[name='AddToCart.chkHyundaiDraw']").length != 0) {
        $("input[value='Add to basket']").click(checkPrizeDraw);
    }
});

function checkPrizeDraw() {    
    if ($("input[name='AddToCart.chkHyundaiDraw']:checked").val() == null) {
        if (!confirm('You have not entered the Hyundai prize draw.\n\nClick \'OK\' to continue with your purchase.\n\nClick \'Cancel\' to return and tick the prize draw checkbox to enter.')) {            
            return false;
        }
    }
}