The United Kingdom’s Conservative Party has said that rules have been changed for the election to choose the party leadership and the country’s next prime minister after an intelligence agency warned that cyber hackers could change ballots, the BBC reported on Wednesday.

The announcement came a day after the Conservative Party members were informed about the delay. The Telegraph had first reported that the delay was due to the warning by the Government Communications Headquarters about possible hacking.

“Your ballot is now on the way – but it will arrive with you a little later than we originally said,” read a part of the message sent to the Conservative Party members. “Please do not worry. This is because we have taken some time to add some additional security to our ballot process, which has delayed us slightly.”

The ballots were earlier due to be issued from Monday. Now, the party has told its members that they should receive their ballot packs this week, PTI reported.

“We have consulted with the NCSC [National Cyber Security Centre] throughout this process and have decided to enhance security around the ballot process,” a Conservative Party spokesperson said. “Eligible members will start receiving ballot packs this week.”

Earlier the plan was that the Tory members could cast their vote either by post or online, and later if they changed their minds, they could use an alternative method to cancel the previous vote.

After receiving the warning, the Conservative Party said it has decided to make changes to the voting, BBC reported. In an email sent to the legislators, the party said that once the ballot company receives a postal vote, it will deactivate the member’s unique codes. This, the party said, is meant to “reduce the risk of any fraud”.

Under this change, members will not be allowed to change their vote.

“It is an offence to vote more than once,” the party’s message to its members said, PTI reported. “Any member found to have voted more than once will have their party membership withdrawn.”

The deadline for registering votes is the evening of September 2. The results will be declared on September 5.

The vote became necessary after Boris Johnson announced his resignation as prime minister on July 7.

On June 6, a no-confidence motion was introduced against Johnson after 54 Conservative Party MPs demanded that he resign. They denounced the parties organised by Johnson and his staff members during lockdowns imposed to contain the spread of the coronavirus disease. The controversy has been famously described as the partygate scandal.

Former British Finance Minister Rishi Sunak and Foreign Secretary Liz Truss are contesting the election.

In the fifth round of voting held in mid-July, Sunak, the former chancellor of the exchequer, got 137 votes while Truss received the support of 113 MPs.

However, Truss is in the lead, according to opinion polls among party members.