Theresa May faces her first electoral test since becoming Prime Minister on Thursday as voters turn out to replace the man she succeeded in Number 10.
With David Cameron gaining 60% of the vote in Witney, Oxfordshire, at last year's general election the Tories were expected to hold the seat comfortably.
Labour was on course to win in Batley and Spen, Yorkshire, in a by-election caused by the death of MP Jo Cox days before the Brexit referendum.
The Tories, Lib Dems, and Ukip decided not to put up candidates in the contest as a mark of respect to the dead MP, but a number of fringe parties, mainly on the hard right, have moved in to try and gain support in the highly unusual election.
Former Coronation Street actress Tracy Brabin was selected as the Labour candidate seeking to carry-on the work of Ms Cox.
In Witney, the Lib Dems are hoping to knock Labour into third place, while the Greens garnered attention with their candidate Larry Sanders as he is the brother of US Senator Bernie Sanders who ran Hillary Clinton a close race in the battle for the Democratic presidential nomination.
Mr Cameron quit the seat last month after insisting he did not want to become a "distraction" to Mrs May while she established herself in Downing Street as he stressed he had his "own views" on certain issues.
The remarks prompted speculation he decided to stand down because the new wave of grammar schools announced by Mrs May was an idea he opposed as PM.
However, Mr Cameron and his successor in Number 10 campaigned together for Tory candidate Robert Courts.
Labour leader Jeremy Corbyn also visited the constituency to back his party's veteran candidate, Duncan Enright, who lost out to Mr Cameron by more than 25,000 votes in 2015.
The Liberal Democrats are represented by businesswoman Liz Leffman, and Ukip by Dickie Bird, in the Oxfordshire seat.
Calls by former Lib Dem leader Lord Paddy Ashdown for a single pro-EU candidate to stand against the Tories came to nothing.