Wondering why most religions operate in the "tax free" zone-when many operate more like a business (effectively, or otherwise).

Somewhere in here:
http://www.legislation.gov.uk/ukpga/2011/25/contents
http://www.legislation.gov.uk/ukpga/2006/50/contents
http://www.legislation.gov.uk/ukpga/1993/10/contents

or "because they always have done"