LONDON — Christians are soldiering on in the battle over God's existence by putting ads on London's famous red buses urging people to have faith.

The posters are a response to an atheist campaign that told people to stop worrying about religion because God probably doesn't exist.

The Christian Party has paid $22,000 to run ads declaring: "There definitely is a God. So join the Christian Party and enjoy your life," in red, pink and orange letters.

The ads will start appearing buses Monday, just as the monthlong campaign by atheists ends. In that campaign, atheists paid for bus ads saying there is probably no God, so "stop worrying and enjoy your life."

The atheist campaign, organized by the British Humanist Association and backed by Oxford University biologist and author Richard Dawkins, sparked a debate over such messages in public spaces.

More than 300 people complained to Britain's advertising watchdog, arguing the atheist ads were misleading and denigrated people's faith. Christian groups decided to respond after the Advertising Standards Authority dismissed the complaints.

"The atheist campaign has been something of a red rag to Christians and was begging for a response," said George Hargreaves, the head of the Christian Party, a religious group that fields candidates for elections to the European Parliament. "I got tired of seeing these messages on buses driving past my window and want to give people the chance to read something with hope."

Another Christian group has also joined the campaign, with a more confrontational message from Psalm 53:1, which reads: "The fool hath said in his heart, There is no God." That ad will run for two weeks.

And the Russian Orthodox Church has joined in with an ad reading: "There is a God, believe. Don't worry and enjoy your life."

Hanne Stinson, chief executive of the British Humanist Society, said the society supported the right of religious groups to post their messages but said the advertisements were "dogmatic and declaratory, leaving no room for reason and debate."

"Our ads were undogmatic and funny, with the addition of the 'probably' in line with the continuing openness of humanists to new evidence," she said on the British Humanist Association Web site.