In 2009, Cadbury changed the recipe of their chocolate to include palm oil. Their reasons were to make it softer to bite whilst still remaining affordable. It's what their customers wanted apparently.
The palm oil issue was not as well known then as it is right now and many activists, who had long been campaigning, set to work to make the public aware about this change and what it meant. Obviously Cadbury were none too impressed, calling us the "vocal minority".
Unfortunately for Cadbury, the public were on our side and they admitted the change in recipe was perhaps a bad idea. They made a big hoo-ha about going back to the original recipe and with clever marketing, everyone thought it was hunky dory.
After looking more closely at their blocks of chocolate, it was discovered that the blocks containing a liquid filling still contained palm oil. Many people, including myself, emailed Cadbury for an explanation.
The use of palm oil in various fillings was part of the recipe before the attempted recipe change in the plain chocolate, so technically what they told the public was absolutely true. They went back to the original recipe of their plain chocolate. But they never changed their filling recipe and it has always contained palm oil.
Cadbury is not palm oil free. Even if you buy the plain blocks, you are funding their purchase of palm oil in Indonesia and are contributing to the current problem.