The Alternative Vote will not deliver more pluralism in British politics. Political competition will still converge around a median, it's just that the position of the median will change to something like Orange-book liberalism.
Choose AV, and British politics will converge around Nick Clegg's position
AV, like FPTP, is incompatible with Britain's pluralist society
AV is not a distant but pluralist relative of FPTP. They are twins