Wakefield and Tiverton and Honiton are going to be huge tests for Boris Johnson, Keir Starmer and Ed Davey.
Lib Dem leader Ed Davey said the PM was partly responsible for rule-breaking and a lack of accountability in parliament.
Conservatives lose hundreds of seats to Labour and the Libs Dems as Sinn Fein is on the brink of making history.
Tory chairman Oliver Dowden claimed Starmer was standing down candidates "in swathes of the country" where Lib Dem support is strong.
Scotland Yard said a "significant" amount of investigative material remains to be assessed, suggesting more might be issued.
Scotland Yard has said it will contact “each individual” who attended parties - meaning both the prime minister and his wife Carrie could face interviews.
District councillor and environmental campaigner Pippa Heylings has been unveiled as the party's candidate to take on the Tories at the next election.
“Now it’s up to us to tear it down," Davey said.
Textbook by-election conditions, but the national picture is less clear
Baroness Williams was one of the gang of four founders of the SDP.