The chairman of the Conservative Party has admitted that not every Tory member will be able to cast a vote in the battle between Boris Johnson and Jeremy Hunt.
Brandon Lewis said the party was still in the process of sending out voting papers to some members yesterday despite the fact the deadline in the race for Number 10 is now just days away.
He blamed administrative issues including problems with updating activists' direct debits and standing orders.
That has meant some people were apparently unaware their membership had lapsed because the party's errors had prevented them from paying their fees.
'Hundreds of people' have reportedly complained to the party's headquarters about problems receiving their ballot papers with staff now scrambling to help as many of them as possible, according to The Telegraph.
Voting in the Tory leadership race will come to a close at 5pm on Monday with the winner of the contest announced on Tuesday and installed as the new prime minister on Wednesday.
The candidates have advised their supporters to make sure their ballot is in the post by close of play today to make sure it arrives before the deadline.
Brandon Lewis said the 'odd person' could miss out voting in the Tory leadership contest
Mr Johnson is the overwhelming favourite to win the contest but the fact that there have been problems, even minor ones, with the voting process is likely to spark controversy.
Mr Lewis said: 'The reality is with 165,000 I'm sure there will be the odd person who feels they should have had a vote who we've not been able to deal with.
'I'm doing everything I can to make sure that, with every power we've got, everyone who is entitled to vote gets one.'
Mr Lewis said he hoped that every member 'who is due a vote gets a vote'.
Mr Lewis's admission came as Mr Johnson said the last three years under Theresa May will seem like a 'bad dream' once he gets the UK out of the European Union.
He insisted he would stick to his commitment to deliver Brexit on October 31.
He also promised to tackle the social care crisis if he becomes prime minister, saying people should not be forced to sell their homes to pay for the support they need.
Mr Johnson used a Daily Express interview to again stress his commitment to leave the EU 'come what may' on Halloween, with or without a deal.
But the scale of the task facing him was laid bare in the Commons on Thursday, as Cabinet ministers who expect to return to the backbenches under a Johnson administration put down a marker about their willingness to cause trouble.
Boris Johnson, pictured in Westminster today, is the prohibitive favourite to be the next PM
But Jeremy Hunt, pictured yesterday, believes he is still in with a shot of causing an upset
MPs voted by a majority of 41 to back a measure aimed at preventing Mr Johnson suspending Parliament in order to force through a no-deal Brexit, with 17 Tories rebelling.
Chancellor Philip Hammond, Justice Secretary David Gauke, Business Secretary Greg Clark and International Development Secretary Rory Stewart all abstained to ensure the move succeeded.
Mr Johnson insisted he could deliver on the result of the 2016 referendum, claiming 'the three years will seem like a bad dream'.
'We'll get on with it and think much more about what we are going to do to unleash the talents and the potential of the whole country, that's what I want to do,' he said.