The country is being offered a vote on it because it is a little better for the Liberal Democrats without being too bad for the Conservatives. However, the pro-AV side needs to keep this sentiment under wraps. So it is interesting that the 6 member steering committee for the putative yes campaign does not contain, as Sunder Katwala points out, a single person who is actually for AV on its own merits. Rather, they all view it as a stepping stone to proper PR.
I suspect that in every debate during the referendum campaign, the first past the post side will demand to know if their opponent thinks AV is the best possible electoral system. It will be hard to persuade the public to change to a system which isn’t even regarded as ideal by the people campaigning for it.