The PM does caveat his well-wishing - adding that "we'll be fighting for the same votes" - but his general effusiveness isn't going to reassure those Tories who suspect he'd quite like a Lib Dem victory, really. Already the murmuring has started, with ConHome's Jonathan Isaby casting an understandably sceptical eye across proceedings, this morning.
What's clear is that this Oldham by-election will be used as a political barometer by all sides. Everything from Cameron's attitude towards his coalition partners to the impact of the student protests will be read, rightly or wrongly, into the campaign and its outcome. The PM will no doubt avoid fuelling the speculation from now on.