Yes, Cameron took a big hit with the Panama papers, and he and Osborne are percieved as part or the financial elite. The gains on opinion still leave labour a long way behind, though I'll admit they are gains. I'm still sticking with the PLP, who represent voters, and a broader section of society.
Dated, but interesting. Look at the dates here, for example:
The collapse is long before Corbyn was leader, and in one case, results improved while he was in power.
How about some more recent reports, though.
April 2016:
https://yougov.co.uk/news/2016/04/08/camerons-ratings-now-lower-corbyns/
Historic tracker of voter intention:
http://ukpollingreport.co.uk/voting-intention-2
Labour trails, but marginally. With the SNP in the position it is in, that's not an "unelectable" Labour.