Hartlepool is an absolute tossup as to who will win
Talk about expectations management.
This seat was easily won by Corbyn even in 2019, and when allegations against the Labour candidate were already known IIRC. BXP voters, who couldn't even bring themselves to vote Tory with that party running on a "Get Brexit Done" ticket, are very unlikely to vote Tory now; in this part of the world they are by and large ex-Labour. Add to that government by-election gains being rarer than hen's teeth.
This seat by all rights should be a Labour hold, even if they have troubles at local level. I doubt it would be fatal to Starmer's leadership, but failure to hold Hartlepool when a more toxic leader managed it would seriously undermine his position. You can imagine the crowing from the nuttiest parts of Labour.
Funny.
Not really, it was a fairly reasonable assumption at the time. The irony is that what happened was easy to "predict" if you don't know much about British politics, but quite surprising if you do (at least the size of the margin, but even the result itself). On Vote UK filled with British anoraks and generally centre-right leaning c. 70% of those voting in the poll thought it would be a Labour hold right up to the final day, including most Conservatives. The media narrative was that it would be a Tory win, but given the low quality of both political journalism and constituency polling in the UK that was hard to take entirely seriously.
No, it wasn't. But it's a good example of things be harder to observe the closer you get up to them.