They joined former Liverpool manager Kenny Dalglish, comedian John Bishop and Liverpool MP Steve Rotheram on the line-up, which was put together under the name The Justice Collective by Robbie Williams' former songwriting partner Guy Chambers.
Some Anglican churches have threatened to break away because of the ordination of a gay bishop by the Episcopal church in the US. Steve Gray of the UCC Indiana-Kentucky Conference said he supports gay marriage but worries about the cost of this decision.