In Mid-Bedfordshire, the seated vacated by Nadine Dorries after she resigned, the swing from Conservative to Labour was 20.5%.
Labour were favourites to win in Tamworth but the Tories were odds-on in Mid Bedfordshire where Labour were as long as 3.412/5 on the eve of the vote.
In the end, however, Labour got the job done in Tamworth and upset the odds in Mid Bedfordshire, causing a political earthquake that will be registered across the UK.
By-election results indicate Tories heading for disaster under Sunak
The latest results are deeply concerning for Rishi Sunak and indicate that his party is heading for electoral meltdown next year. They are 3.185/40 to lose more than 200 seats.
For Keir Starmer there was delight and further proof that he is destined to enter Downing Street to be Labour's first prime minister since 2010.
Starmer is 1.182/11 to be the UK's next PM and the only reason to oppose that is the possibility that Tory MPs may look at last night's results, as well as Sunak's dismal personal polling, and decide they cannot go into a general election with him as their leader.
That seems unlikely, however, and Sunak looks set to lead the Tories to a defeat on the scale of the one they endured under John Major in 1997.
Starmer said today that voters were "crying out for change." The Conservatives look determined to cling to power for as long as possible and October to December next year is 1.434/9 in the Exchange's date of next general election market.
This week's by-election results are further evidence that it is a question of when not if the Conservatives suffer a catstrophic defeat.