Campaigning in the Hartlepool by-election, Sir Keir Starmer said repeatedly that Labour had a “mountain to climb” if it was to regain power. Now that the votes are in and counted, that task looks every bit as formidable as the party seeks to chart a route back to No 10. It is hard to see the result as anything other than a personal blow to the Labour leader in his first major electoral test since he was elected a little more than a year ago. Hartlepool has been Labour since the seat was created in 1974 and its loss is another damaging breach in the once impregnable “red wall”.