John Curtice on Tamworth and Mid Bedfordshire results
Sir John Curtice said Tamworth gave a "straightforward " message to parties, while Mid Bedfordshire offered a "somewhat different pattern".
He said governments "do not routinely" lose by--elections of swings bigger than 20% but there have been three results of that scale in this Parliament.
The professor of politics spoke to Jo Coburn on Politics Live about comparisons to by-elections in the John Major government in the 1990s.
