With the pro-AV campaign likely to be run out of Cowley Street, or at least by LibDem proxies, it seems wise to choose someone who is not a Conservative Party figure, not least because he will have to win Labour and union support for the campaign as well as keep some of the more ambivalent Tories onside. The aim is to assemble the strongest, broadest based campaign possible to oppose AV regardless wider of ideological differences.Given that there is a significant knee-jerk anti-AV tendency amongst Labour supporters who simply want to put one over on the Lib Dems this appointment (from a Rightie perspective) looks tactically clueless. The TPA is about as popular with Labour supporters and union members as hunt saboteurs are with the Countryside Alliance. It's like magnetic repulsion. So appointing the head of TPA to this campaign will surely tip many of those who are only against AV because the Lib Dems are for it back in the other direction. And that in turn may help rapproachement with the LDs.
If I were a pro-AV Lib Dem I'd see this appointment as a plus point, and I'd be hammering it home with Labour supporters as often as possible.