Isaac Levido, the former right-hand man of Lynton Crosby, has taken centre stage at Conservative headquarters (CCHQ) as head of the campaign, replacing his former boss in the election war-room as the party targets 50 key seats and defends another 50 marginals.

Tory insiders said Levido – little known either inside or outside Westminster – has taken a desk in the middle of the office, known as the central “pod of power” occupied by Crosby in previous elections.

Dominic Cummings, the prime minister’s de facto chief of staff, will not officially be running the campaign and is still based in Downing Street, according to several sources. He is due to have an operation in November, which was previously delayed, and it is understood that this may still go ahead during the campaign.

Over at Matthew Parker Street, the Conservative party’s headquarters, Levido is sitting next to Michael Brooks, a pollster who worked with him on Scott Morrison’s unexpected victory for the Liberals in Australia earlier this year, and the two young New Zealanders, Sean Topham and Ben Guerin, who are running the campaign’s digital media strategy. The pair previously helped run a controversial Facebook propaganda network while working as contractors for Crosby’s CTF Partners.

Alongside them sits Darren Mott, the director of campaigning and a veteran Tory with experience of battleground seats, who had to make room for Levido when the newcomer was appointed over the summer.

Those who have worked with Levido say he is less of a big character than Crosby, but was his most trusted lieutenant. In 2015, there was a running joke in the office that Crosby was constant calling out “IS-AAC” across the room to summon his protege for advice.

Boris Johnson and Lyton Crosby at the Spectator’s summer party in 2012. Photograph: Alan Davidson/REX/Shutterstock

A former colleague of Levido said: “He was Lynton’s right-hand man in previous campaigns. He’s seen up close what it takes. He’s understated, quietly effective, very much out of the Lynton Crosby textbook. But he won’t be seeking the limelight and recognises that it’s a big task and is definitely not taking things for granted.

“He just came back from doing the Australian election won against the odds and it was very reminiscent of here in 2015 when people said you can’t win and the polls were saying that, but the private polling was much more consistent with him winning. And there’s a recognition it will be a digitally focused campaign.”

Crosby himself is not expected to be a presence in CCHQ like he was in 2017, when he clashed over strategy with Theresa May’s advisers, and 2015, when he ran the campaign that saw David Cameron get a surprise small majority.

He is an old friend of Boris Johnson, having run his London mayoral campaigns, and the pair were in touch by phone for informal advice during his Conservative leadership campaign. Downing Street declined to reveal details of who would be involved in the campaign at this point.

Tory insiders claim they are more advanced in their preparations than they were in 2017 but there is nervousness among many MPs about the strategy of targeting Labour leave-voting seats in the north, Wales and Midlands that May failed to take in 2017.

There are also nerves about losing seats across Scotland to the Scottish National party and struggling against the Liberal Democrats in the south-west. The anxiety about holding on to current seats means the party’s resources will be split between an offensive and defensive strategy.

Matt Hancock, the health secretary, appeared to reveal four key target constituencies for the party as he mentioned in a broadcast interview that new cancer treatments are being rolled out “from Barnsley to Bassetlaw; from Wigan to Warrington” – all of which are northern leave-voting Labour constituencies.

A Guardian analysis of marginals where the Tories are likely to be targeting Labour show the party has selected candidates in almost all of them. The rows over candidate selection are centred on plum seats with big majorities where MPs are standing down.

Charles Walker, a vice-chair of the 1922 committee, resigned from the party’s board earlier this week following a furore about attempted interference by Downing Street in the selection process. A Tory source said he had rowed with Dougie Smith, a CCHQ official, over attempts to centrally impose candidates and then walked out.