Here’s the link to the government website announcing that automatic information exchange is under consideration, and the PDF writeup on the topic. The Guernsey tax authorities are marching in step with the rest of Europe towards proactive sharing of tax information between governments.
Don’t worry too much about the details of what is happening in Guernsey. At least at the moment. Let’s get all metaphorical: ignore the ripples; watch the tide.
What’s coming at you
Stand back and look at trends. They are pointed clearly in the direction of proactive sharing of information across borders. Banks are required to collect data. Governments agree to share that data.
Think of the way you get a Form 1099 from a U.S. bank stating how much interest you earned. This gives the IRS a way to verify that you are telling the truth on your income tax return. You should expect that governments will be trying to get as close as possible to this result for cross-border investments.
It will not be easy to get there — the political impediments are obvious. So, too, are the technological problems of exchanging vast amounts of data between governments. This is going to take several years (at least).
(For an interesting side-note to why data processing difficulties might keep the Eurozone intact notwithstanding everything else, check out this post by the Chief Astronaut of the Cardboard Spaceship).