A flight believed to be carrying former British Prime Minister Boris Johnson has landed at London's Gatwick airport, according to flight-tracking website Flightradar24.

Sky News reported that Johnson was on the plane back to Britain as he considers an attempt to win a second term as prime minister after Liz Truss quit last week.

According to Flightradar24 data, the British Airways flight he is believed to be on, BA2156, was the most tracked flight on the website with about 6,800 people viewing it.

The plane was also shown landing at the Gatwick airport on Sky News.

It would mark an audacious attempt to return to power by Johnson, who only left office early last month, after dozens of resignations from his government following a slew of scandals led to his departure.

Conservative leadership rival Rishi Sunak reached the minimum threshold to contest the UK's top job.

Sunak's allies in parliament said he had garnered the nominations of 100 Conservative MPs, the threshold set by the party to stand.

However, both Sunak and Johnson are yet to announce they are running, leaving it to allies to signal their intent. (Reuters/AFP)