Last year it did quite openly profess (admittedly limited) support for the Liberals:
http://www.independen...e-missed-1962527.html
You can also check out this MORI poll of newspaper readers during each election from 1992 to 2010 - while not completely, it seems Independent readers do swing to the left a little on average:
http://www.ipsos-mori...922010.aspx?view=wide
I take your point about red-tops, but I'm not sure the high-end press are quite as partisan as you're making out. The Times isn't particularly partisan, but is slightly centre-right. Though I guess what you're saying is true of the Telegraph. But I still think my point stands. A paper backing a horse at a general election is fairly common (and kudos to the Ind for refraining by and large), but what I mean is consistent 'x party is AWESOME' vs 'x party is TERRIBLE' themes in papers. They tend to be fairly critical of all parties which don't meet whatever their political ideals are even if they usually support them at elections - as, for instance, the Guardian would often do with Labour.