frannyp:

I think Michael turned round when the vicar saw Cain and Debbie standing at the back and said there were places at the back so he didn't hear her say 'Mum'.  

No, I'm pretty sure he saw them before the vicar did, because he was facing towards the back of the church after half hugging Charity. I think it was Michael looking towards the back of the church that made the vicar look.