The Great Outdoors Church Service is designed to show solidarity with persecuted Christians around the world, who are not able to worship in a church.
This will be its fourth year, as it sends a message of hope to suffering believers.
Andrew Boyd, from Release International, told Premier. "Churches are being burnt down by militants, we're seeing that happen in Nigeria, we've seen it in Iraq and we've seen it happen elsewhere - so people are forced to worship out of doors in the open air."
"It's not just an issue of what the weather's going to be like, but in order to keep their faith for witness before God, they have to come back, literally, to places where authorities are waiting for them or militants could be standing by waiting for them and put them in that place of risk, in order to worship publicly."
Mr Boyd also told Premier about a protestant church in China that has been forced to worship outside after they were banned from worshipping in buildings. They now gather in a park.
He said: "You look out the window of your apartment on Sunday morning and there be a police man down in the road looking back at you, today could be the day when you are going to be the one arrested making your way to the park."
Listen to Premier's Hannah Tooley speak to Andrew Boyd here:
