People want a party pretty much in the middle, the same as they did last year and will want in 2020. Just because the Tories have been absolutely dire doesn't mean that people won't vote the same way in what they hope will be a centrist party with competence.
The simple truth is Blair appealed to that ground and looked competent, so he got 3 terms. Cameron alo not looking pie articulately competent for last years election, obviously still had the beating of ed milliband.
Nothing stopping the Labour Party occupying that ground again and introducing a few left wing tweaks, but if they don't look competent they haven't a hope. Add to this if remain win, there will be a eurosceptic party of some kind on the voting cards and this could cause trouble for both labour and Tories, particularly labour as they have pretty much set their sail for closer eu integration, whereas the Tories can still be looked at as a party with a decent % of euro scepticism