That's interesting. I'm of course comparing in my mind to the three Romney presidential campaigns, where it was definitely a factor, but there are a number of reasons I can imagine that would explain the difference.
Religion seems to play a far more understated role in British politics compared to America, it's often far less explicit and it's quite rare for a candidate's religion to have a large direct impact on votes (even if it may have indirect impacts through a candidate's views towards certain issues, e.g. Tim Farron)