Labour support fptp because they fear the Tories

We can see why the Conservative party would have a preference for fptp as it is the only means by which their policies are relevant. The Tories cannot get elected without fptp so they will never agree to its replacement. It is the opposition Labour party who are in a position to change the voting system because it is not so detrimental to their beliefs to have pr. The Labour party are generally perceived as the more progressive of the two main parties. (They do not describe themselves as conservatives.) So to change the voting system is not antithetical to their philosophy. It would be consistent with the progressive ideology for the Labour party to change the voting system but they will not do so. It is hard to find an explanation for why the Labour party are reluctant to change the voting system but perhaps it is because they are (irrationally) scared of the Tories.