Boris Johnson is threatening to set an “early test” for his successor by ensuring they have to face two early byelections as the new Tory leader, the Observer has been told.

The prime minister is planning to elevate at least two current MPs to the House of Lords well before the next election, triggering two contests that will test public support for whoever replaces him in Downing Street.

It is understood that he wants to hand peerages to Nigel Adams, a cabinet office minister and one of his closest allies, and culture secretary Nadine Dorries, who has emerged as one of his most loyal cabinet colleagues. Both have large majorities, but the combination of a recent Tory poll slump and its disastrous recent byelection record could make the contests a close call.

There are currently two lists of peerages planned – one is a regular list, while the second is Johnson’s resignation honours list. “You can’t announce a peerage and say they won’t kick in for two years [after the next general election],” said a source familiar with Johnson’s plans. “Elevating MPs will mean those seats will be freed up to be contested. It will be a very early test for the new leader.”

Adams, who championed Johnson long before he became Tory leader, has already announced he is stepping down at the next election. As minister without portfolio in the cabinet office, he was at the heart of attempts to rescue Johnson’s premiership as it was falling apart earlier this month.

He has held his seat of Selby and Ainsty three times, each time with an increased majority. He won the seat by more than 20,000 votes at the last election. Labour is the challenger and a byelection could show Keir Starmer’s party is closing the gap. Dorries holds the seat of Mid Bedfordshire, with a 24,000 majority at the last election.

It comes with persistent rumours that Johnson is planning a major list of peerages, which is expected to include the former editor of the Daily Mail, Paul Dacre. Johnson had been determined to make Dacre the chair of broadcasting regulator Ofcom, but the appointment was opposed by an independent selection panel. Dacre subsequently pulled out of the process. Some new peerages are expected to be announced this summer, but are first vetted by the House of Lords appointments commission.

Johnson has previously provoked criticism over his peerage appointments, having already nominated Lord Moore of Etchingham, his former editor at the Daily Telegraph, and Evgeny Lebedev, the Russian-born businessman and son of a former KGB officer.