Voters are going to the polls to elect new MPs in Kingswood and Wellingborough.
The by-elections will decide who will replace former Conservative MPs Chris Skidmore and Peter Bone, with both seats won by the Tories at the last general election in 2019.
Polling stations opened at 07:00 GMT and close at 22:00, with results expected from early on Friday morning.
Constituents will need photo ID to vote.
The Northamptonshire seat of Wellingborough had a Tory majority of more than 18,000 at the last election, while in Kingswood, which is near Bristol, the party’s majority was more than 11,000.
There are 11 candidates on the ballot paper in Wellingborough and six in Kingswood.
Polls have opened in the Wellingborough and Kingswood byelections, seen as a final chance for Rishi Sunak to buck predictions that his party is heading for a landslide defeat at the next general election.
Labour is expected to win both contests. The party has pulled off a string of byelection victories, gaining four Tory seats in a row since July.
A win for Labour would temper fears that a tough week for the party has significantly threatened its electoral prospects. A win for the Conservatives could give Sunak a lifeline and stave off any long-shot attempts by backbenchers on the right of the party to replace him before the general election.
I had great hopes for Boris and the Conservatives after the 2019 election, but it has been a disaster of their own making
Does anyone really believe things will get better under Labour? – they have been famously described as two cheeks of the same arse
The real problem is that we are governed by traitors - why on earth can’t Reform, UKIP, and similar patriotic parties sort themselves out, and join up to form one party that will do the best for the UK?
What would change is that we’ll be governed by a party and leadership that hasn’t proved itself a corrupt, lying, self-serving chumocracy during it’s time in office and during Covid
That, like Johnson getting chucked out, will at least be a breath of fresh air and a fresh start.
Getting rid of the putrid current incumbents has got to be better than letting them carry on shaming our democracy?
What sort of hand a Labour government would make of it is yet to proved, but they couldn’t be any worse, at least we’d stand some chance
