Here is a few lines from the Christian Institutes booklet - find more by following the link below.
"The referendum to change the voting system for elections to the House of Commons takes place on 5 May. The question is whether to adopt the ‘Alternative Vote’ system (AV) instead of the traditional ‘First Past The Post’ system.
However low the turnout, the referendum decision will be binding. If the majority of those voting back AV then that system will be implemented for elections to the House of Commons across the UK. So one way or another, the AV referendum will be decisive. It is therefore important that Christians vote."