More than a thousand Conservative members have been issued with more than one ballot paper to vote for the next party leader and prime minister, threatening to bring the contest into disrepute.

Reports suggest that more than a thousand voters could be affected by the blunder, with party insiders revealing a series of errors that have led to duplicate ballot papers being issued.

It comes as a YouGov/Times poll of Tory members showed Johnson leading Hunt in the leadership race by 74 per cent to 26 per cent.

Ballot papers have been dispatched to around 160,000 Conservative Party members around the country to choose between Boris Johnson and Jeremy Hunt as the next leader and Britain's next prime minister.

The vote closes on 22 July, with the result announced the following day.