Discount Codes

I have set up discount codes on our site for testing we have one called “upgrade”
that applies a £35.00 off at checkout.

Website is http://www.telephone-support.net

This all appears to and the discount is applied, but when we do a guest checkout and change the country to UK fro Afghanistan then it wipes out the discount code and resets the price to the normal price.

So then we add the discount code again and then it reset back to Afghanistan.

So we cannot apply a discount code to any of our items, Any ideas please.

PS .
Is the also anyway to change the country default to UK