I just bought domestic tickets on the Peruvian version of the LAN site - cheaper than the UK version. All went fine until I had to put in my credit card. It came back with the 'Verified by Visa' prompt, but then gave an error message.
I called LAN in Peru, and sorted it over the phone - mentioning that the credit card was registered in the UK, and I'm neither UK nor Peruvian - but that didn't seem to be a problem.
Now we'll just have to wait until we check in