I would not be so sure that Lab are as keen behind the scenes as they are in public for a GE especially after they not only failed to capitalise on the appalling showing from the Cons in the locals but actually managed to lose councillors compared to Miliband's previous poor showing. Add in Farage sniffing around leave constituencies and there is even more danger for the main two that they will lose more than they gain by calling a GE.
It's only an election for one seat out of 650. Wait until there is something more substantial to fight for before becoming too pessimistic and writing them off.