Prime Minister Cameron praised Church leaders and volunteers in his video message, which urged people to speak out for Christians "persecuted for their beliefs".
The Prime Minister said Britain had been built on the Christian beliefs of "responsibility, hard work, charity, compassion, pride in working for the common good, and honouring the social obligations we have to one another, to our families and to our communities."
"These are values we treasure," he continued, saying that it is those beliefs which give Britons the strength to say: "Yes, we are a Christian country, and we're proud of it".
Cameron added that these values speak to "everyone" in Britain, to people of all religions and none, and praised those who work for social good and to help others.
Referring to the terrorist attacks in Brussels earlier this week, Cameron said Britain must show it will "never be cowed by terror".