Delivery of ballot papers for the Tory leadership contest has been delayed after concerns were raised over hacking concerns.

Intelligence from the UK’s security services at GCHQ suggested that people’s ballots could be altered through online interference.

Postal ballots are yet to be issued to the around 160,000 party members, who will choose Boris Johnson’s successor this summer, as a result of the GCHQ concerns.

The ballots were due to be sent out from Monday, but members have now been warned they could arrive as late as August 11, The Telegraph reported.

Key changes have been made to voting rules in the wake of GCHQ advice, meaning the Tory faithful now only have one chance to cast their ballot.

Under the original system, party members were allowed to vote but change their decision while the ballot remained open but now a unique code will be provided which will only allow one, unchangeable vote, the paper said.

It is believed that the the danger of a cyber attack is not being posed specifically by another country or opponent but it is more general advice over the vulnerabilities of the voting process.

Liz Truss has moved significantly ahead according to a latest opinion poll

Liz Truss has moved significantly ahead according to a latest YouGov poll

Allegations have been made before of other countries including Russia and China being involved in trying to manipulate opinion polls and elections, including the 2020 US presidential elections.

“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 cyber security guidance and support,” a National Cyber Security Centre spokesman told The Mirror.

“As you would expect from the UK’s national cyber security authority, we provided advice to the Conservative Party, on security considerations for online leadership voting.”

Tory members have received messages telling them that there is a delay in the voting due to security concerns – which were not outlined.

It reportedly read: “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 ballots for the leadership ballot were due to be sent out last Monday

The ballots for the leadership were due to be sent out last Monday

North West Durham MP Richard Holden, who is supporting Rishi Sunak, told BBC  Newsnight: “I’ve heard they’re delayed.

“I think there’s some minor security issue which has been dealt with but it won’t delay the result of the poll which is a crucial thing for everybody.”

A Conservative spokesman said: “We have consulted with the NCSC throughout this process and have decided to enhance security around the ballot process.

“Eligible members will start receiving ballot packs this week.”

In the leadership race Liz Truss has increased her advantage over rival Rishi Sunak to 34 points, according to a YouGov poll of Conservative Party members.

It shows 60% of the party members polled between July 29 and August 2 say they intend to vote for Ms Truss, the Foreign Secretary, up from 49% in the period July 20 to 21, which was immediately after the final two were announced.