The prime minister alleged that “millions” of additional voters who could be expected to vote against Brexit would be added to the electoral roll for any rerun vote.
He appeared to be referring to suggestions that EU nationals and 16- and 17-year-olds might be allowed to take part in a Final Say vote.
Labour’s manifesto promises to reduce the voting age to 16 and grant voting rights to all residents of the UK, though it does not make clear whether these changes would be in place in time for the referendum the party plans for June next year.
Speaking during a visit to a factory in Matlock, Derbyshire, Mr Johnson denounced as “bizarre” Jeremy Corbyn’s plan to renegotiate a Brexit deal within three months of the 12 December general election before putting it to a public vote after six months.
“We would have six months or a year for another referendum campaign on this weird deal he wants to do, and I think people will be outraged by the whole thing,” said the prime minister.
“To think it’s going to be rigged in some way by getting millions more voters who would be very likely to vote one way rather than the other ... I think that would cause a great deal of public disquiet and I don’t think it’s the right way forward.”
Mr Johnson’s comments echo the warning of his senior aide Dominic Cummings, who last month suggested that Mr Corbyn would join Scottish National Party leader Nicola Sturgeon in a hung parliament to “cheat” a second referendum.
In a blogpost, the former Vote Leave supremo wrote: “If this Corbyn-Sturgeon alliance takes control, their official policy is to give millions of EU citizens the vote in the second referendum.
“They don’t plan to lose again and they’ve literally written into their manifesto that they will cheat the second referendum.”