function empty(elem) {
  if (elem.value == null || elem.value.length == 0) return true;
  else return false;
} 

function check(form) {
  var error = '';
  if (empty(form.location)) error += '  - Location\n';
  if (empty(form.req_from_day)) error += '  - Required from Day\n';
  if (empty(form.req_from_mth)) error += '  - Required from Month\n';
  if (empty(form.req_from_yr)) error += '  - Required from Year\n';
  if (empty(form.req_til_day)) error += '  - Required until Day\n';
  if (empty(form.req_til_mth)) error += '  - Required until Month\n';
  if (empty(form.req_til_yr)) error += '  - Required until Year\n';
  if (empty(form.party_number)) error += '  - Number in Party\n';
  if (empty(form.adults)) error += '  - Names of Adults\n';
  if (empty(form.pcontact)) error += '  - Party Contact\n';
  if (empty(form.address)) error += '  - Home Address\n';
  if (empty(form.postcode)) error += '  - Postcode\n';
  if (empty(form.tel)) error += '  - Contact Tel.\n';
  if (empty(form.email)) error += '  - E-mail\n';

  if (error != '') {
    alert('Please enter a value for:\n' + error);
    return false;
  }
  else return true;
}