The delivery of ballot papers to Conservative members to vote for the next prime minister has been delayed following security concerns. The postal ballot packs were due to be sent out from Monday to about 160,000 Tory members to choose between Liz Truss and Rishi Sunak. However, members have been informed the ballot papers will arrive later than scheduled and could arrive as late as 11 August. An email on Tuesday evening said: “Your ballot is now on the way – but it will arrive with you a little later than we originally said. “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 announcement of the leadership contest is due to take place on 5 September, which is expected to remain the same despite the delay. The decision to delay the sending out of the ballots follows advice from the National Cyber Security Centre (NCSC), part of the UK’s GCHQ listening post. An NCSC spokesperson said: “Defending UK democratic and electoral processes is a priority for the NCSC and we work closely with all parliamentary political parties, local authorities and MPs to provide cybersecurity guidance and support. “As you would expect from the UK’s national cybersecurity authority we provided advice to the Conservative party on security considerations for online leadership voting.” The government communications headquarters, known as GCHQ, apparently warned of a security risk in which hackers could change Conservative members’ ballots, according to the Daily Telegraph, which first reported the story. The email to Conservative party members states they will have the option to vote by post or online, with codes to be deactivated once the vote has been received for the latter option to reduce the “risk of fraud”. It adds: “To vote online, simply input the unique one-use codes printed on your ballot paper and fill in the security questions. Once used, your codes are invalid and you won’t be able to re-enter the site. “If you decide to vote by post … once received by the ballot company we will deactivate your online codes.” Sunak trails Truss in Tory membership polls, and while some recent polls have shown the gap to be narrowing a YouGov survey for the Times on Tuesday gave the foreign secretary 60% support with the former chancellor on 26%.