Answer:
They were furious, especially their king and members of government. They believed that colonists betrayed them. On the other hand Declaration meant that Britain will lose its most important territory and therefore announced that colonies are in the open rebellion and wanted to prevent them from seceding.
Step-by-step explanation:
British government didn't understand the needs of colonists. They imposed many taxes, didn't respected them as citizens of Crown, but were either unaware or didn't expect that the rebellion could happen.
So, when the Declaration was announced it was seen as an act of treason.