Problem is how many people go to church now, they only turn up for Songs Of Praise to get on the tele. If you hang around Scout huts or the Girl Guides you are likely to get arrested.
Looks like the best place and where modern Britain congregates and prays is Tesco. If you have the bottle how about setting up in a Tescos car park with some old carpet and gaining customers that way?
Just get one of those Gazebo thins from B&Q and you are away, millions of customers every hour, be even better if you could over Tesco Club Points, you would not believe what my girlfriend will do for 50 extra points on her card.