A very broad history of election campaigns in the UK (which we have a limited dataset!) shows that there have only been what 2 elections since 1945 when an unpopular government in poor form has been be able to run an inspiring and winning campaign; and in both those there was a Liberal/SDP/Lib Dem vote to squeeze & a labour leadership not trusted...
Of course, the only election in which a party has actually been able to overturn a comparable polling deficit to the one the Tories now face was 2017 when Labour did it, but they had the advantage of being an opposition facing an incumbent government who were running a completely cack-handed campaign.