Hundreds of Conservative party members have been sent more than one ballot paper in the party leadership contest between Boris Johnson and Jeremy Hunt. 

Those that registered their home and work address, or that have changed their name, are likely to receive more than one, according to a party source.

However, Conservative party rules state that they should vote on a ‘one person, one vote’ basis.

Voting has already begun in the contest with frontrunner Boris Johnson expected to take a landslide victory with up to 74 per cent of the vote. 

A source said more than 1,000 people could have been sent several ballot papers, reports the BBC, out of a 160,000 party membership.

In a briefing paper issued last month it is made clear that voters are expected to cast their ballots only once. 

However, the leadership election is not monitored by the Electoral Commission, which is responsible for ensuring that votes are cast freely and fairly

Former Cabinet minister Sir Patrick McLoughlin, who is chairing Mr Hunt’s campaign, said the issue has ‘got to be looked at’ but that he expected party members to follow the rules.

Sir Patrick, who is also a former Conservative chairman, told the BBC’s Today programme: ‘It’s made very clear on the ballot paper that you are only allowed to vote once. I expect Conservative members to follow that.

‘If people have joined two associations they may get two ballot papers. I get two ballot papers in elections because I am on two different sets of electoral registers, it doesn’t mean that I vote twice, I don’t.’

‘It can’t be clearer, it’s right there on the ballot paper saying that you must only vote on one occasion and I expect people to do that’.

Iain Duncan Smith, chairman of Mr Johnson’s campaign, said the Tory Party needed to make sure it could address the problem of multiple ballot papers being given to members.

‘Obviously there is an issue here, I accept that,’ he said, adding that he was sure party chairman Brandon Lewis was looking at it.

‘In all elections there are issues about this, where people are registered separately, and in the ballot papers it’s quite clear … that you are not to vote more than once.

‘But it’s clear that the Conservative Party needs to continue to do some work and look into how they can actually sift this properly so that they recognise who is who.’

The vote will close on July 22 and the result will be revealed a day later.

A YouGov poll has suggested that Boris Johnson will be the clear winner.

This morning, as members start to cast their votes, they have been tweeting out their ballot papers showing their support for both the election candidates.

Jeremy Hunt has pleaded with voters, asking them to hold-off until after the debate on Tuesday. 

Theresa May will take her final session of Prime Minister’s Questions on July 24 and hand over to the contest winner that afternoon.