Norris: Praised more democratic system
The ballot is the first time all 300,000 party members have been able to vote for their leader and reports of anomalies in the system emerged on Thursday.
Tory vice-chairman Mr Norris played down the anomalies, which he insisted would not affect the outcome of the contest.
Three month deadline
Anyone who was a party member on 28 March is eligible to vote in the leadership battle between Ken Clarke and Iain Duncan Smith, which ends at noon on 11 September.
John Strafford, chairman of pressure group the Campaign for Conservative Democracy, said he was worried by anomalies revealed by BBC Radio 4's Today programme.
"Whenever a major political party is brave enough to go down the democratic route it finds teething problems," said Mr Strafford.
"We have seen a lot of teething problems in this election and in particular regarding this question of subscriptions."
UKIP eastern regional organiser Tom Wise said his party had many members that had defected from the Conservative Party but whose Tory subscriptions had not yet expired.
They might well receive ballot papers - and act upon them, he said.
'Inaccurate members'
The programme also heard from a woman, who did not give her name, who said she had received ballot papers despite never being a Tory member.
"I can only think that the Conservative Party have got inaccurate records," she said.
"The only other reason I can possibly think is that my husband is a member of the Conservative Party and they assumed I was too."
Essex Conservatives' chairman Stephen Castle forecast disappointment for many Tories who expected to be able to vote.
"The difficulty comes where there are bound to be some members or people who perceive themselves to be members who perhaps joined through Conservative clubs and perhaps whose membership has lapsed," he said.
'No impact'
But Mr Norris insisted the reported irregularities would make no difference to the contest.
"The reality is I don't think any of this is going to have the slightest impact on the outcome," he said.
"The overwhelming number of members have got their ballot papers and actually what is interesting, I think, is that the vast majority of them will return them within 72 hours."
He praised the democratic way in which each party member's vote now counted as much as that of outgoing Tory leader William Hague.