It's a mid-term bye-election, and turnout was about half the size it was at the last GE. The drop in Tory votes is easily identified as the result of thousands of voters staying at home. There's literally no reason for Labour to celebrate this "result" - it's the political equivalent of slicing a shot towards the corner flag when you're twelve yards out from an open goal.
The problem for Labour is that they have so few front bench "big guns" who can be wheeled out for campaigning - Starmer, Rayner, Lammy, Thornberry and co are all massive turn-offs to voters. Bringing Sadiq Kahn out in that area would also have backfired dramatically.
It's terrifying that even when the Tories are up to their armpits in bad press, poor performances and open sleaze, Labour still can't appeal to Mr. Average as an alternative.