function checkform()
  {
    valid = true;
    mess = 'Please correct the following problems before sending your message:\n\n';
    
    if (document.webmail.yourname.value == '')
      {
      mess = mess + '- Enter your name in the \'Your Name\' box.\n';
      valid = false;
      }
      
    if (document.webmail.telephone.value=='' && document.webmail.emailaddress.value=='')
      {
      mess = mess + '- Enter a telephone number or an email address (or both).\n';
      valid = false;
      }
      
    if (document.webmail.telephone.value!='')
      {
      telephone = document.webmail.telephone.value;
      var nums = /^[0-9]+$/;
      if (!telephone.match(nums))
        {
        mess = mess + '- Use only numbers in the telephone field.\n';
        valid = false;
        }
      }
    
    if (document.webmail.emailaddress.value!='')
      {
      emailaddress = document.webmail.emailaddress.value;
      var emailExp = /^[\w\-\.\+]+\@[a-zA-Z0-9\.\-]+\.[a-zA-z0-9]{2,4}$/;
      if(!emailaddress.match(emailExp))
        {
        mess = mess + '- Our system does not recogise this as a valid email address.\n';
        valid = false;
        }
      }
    
    if (document.webmail.message.value=='')
      {
      mess = mess + '- You have not typed anything in the message box.';
      valid = false;
      }
      
    if (valid==false)
      {
      alert(mess);
      }
      
return valid;
  }