I think it’s too early to say definitively and I don’t like the idea of volunteers who want to safeguard elections having motives unfairly questioned. I don’t think we can say the result of the by-election should be questioned, but we absolutely should take accusations of malpractice, like observed family voting, seriously and without ascribing motivations to them when there us no evidence of such. It was bad enough when the Tories hurled accusations of lefty lawyers with agendas, it would be bad here to do so against election observers, with no known ties to any party. It would be one way to sow discord and distrust in a system. And if we let standards slip, it opens doors to more accusations and them getting traction.
If anything went wrong with officials on the day, it wouldn’t necessarily be because of anything malign.