I don't think Labour will be overly unhappy at the Tiverton result. They will be cock a hoop that this is another mail in the Tory coffin. We are getting to the point where tactical voting doesn't need to be hugely coordinated for Tory deselection to happen.

I'm sure both Labour and the Lib Dems realise that at the present time tactical voting is the only way to unseat the Tories given the structure of the First Past The Post System. For both parties and the country as a whole to benefit they understand the priority is to remove the Tory government first.