Magento – Get the country code of website user

Try like that (in some phtml file, but you can rearange it to fit only in your php function):

<ul>
  <?php foreach(Mage::app()->getWebsites() as $website): ?>
    <?php foreach ($website->getGroups() as $group): ?>
      <?php $stores = $group->getStores();
        foreach ($stores as $store): ?>
        <li class="<?php echo Mage::app()->getStore($store->getStoreId())->getCode();?>"><a href="<?php echo Mage::app()->getStore($store->getStoreId())->getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK);?>"></a></li>
      <?php endforeach; ?>
    <?php endforeach; ?>
  <?php endforeach; ?>
  </ul>

Now, with $store->getStoreId() you are able to get the store id.

Step 1: Create your initial Rule

• Add the Condition Shipping Country is not United Kingdom
• Add a Priority e.g. 5
• Add the Discount

Step 2: Create a Second Rule

• Add the Condition Shipping Country is ... <- Leave the Country Empty
• Add a Priority e.g. 3 (should be lower the the Priority from Rule 1)
• Choose in the Action Tab Stop Further Rules Processing = Yes

Explanation

The Second rule serves as a "Stop-Rule". What happen is, the Stop Rule has an lower Priority, so this rule fires first. For a new User the Condition of the Rule is true, because the shipping country is ... (empty). And then it stops all further Rules.
If the first Rule is true, shipping country != GB (the second rule is automatically false). So, the customer gets the discount.

This solution doesn't affect other rules, because the default priority is 0.