Two political campaigners hired by the Conservatives to run their digital campaign at the next general election previously helped run an enormous Facebook propaganda network.

Sean Topham and Ben Guerin have been employed to improve the party’s online operations, following a disastrous 2017 election when the Tories were outgunned by Labour in internet campaigning.

This summer, it was revealed how Sir Lynton Crosby’s CTF Partners used Facebook to run a large-scale professional disinformation network on behalf of paying clients including major polluters, the Saudi Arabian government, anti-cycling groups and various foreign political campaigns.

Documents seen by the Guardian show that Topham and Guerin, while working as contractors for CTF Partners, had oversight of dozens of these pages which sidestepped Facebook’s rules on transparent political campaigning, reaching tens of millions of people on behalf of paying clients while appearing to be grassroots independent news sources. All parties have previously pointed out that they operated entirely within the law.

The new Conservative digital campaigners, both New Zealanders in their 20s, also flew around the world to promote the interests of clients such as Glencore, one of the world’s biggest miners, while concerns – which they strongly denied - were raised about some of their behaviour in the office.

The pair’s arrival comes after their success helping Australia’s rightwing coalition unexpectedly win the country’s general election, where they were praised by local media for their understanding of how to fight online campaigns. Purposefully low-quality memes based around popular shows such as Game of Thrones were used in a bid to drive interactions – good or bad – at any cost, on the basis that this would boost the reach of future Facebook posts.

“We’d make them really basic and deliberately lame because they’d get shares and lift our reach; that made our reach for the harder political messages higher,” an anonymous individual told the Sydney Morning Herald, dubbing the strategy “boomer memes” as the content appealed to older audiences.

In recent days, the Conservatives have begun purposefully posting badly-designed social media material, at one point urging MPs to back a Brexit deal using the often-derided Comic Sans font. The Tories’ political opponents lined up to mock the image, inadvertently sending it viral and ensuring it was seen by a wider audience.

Conservatives (@Conservatives) Now is the time for MPs to back the new deal and get Brexit done.#GetBrexitDone pic.twitter.com/JuqaOVdlMC

The hiring of the two New Zealanders comes as transparency campaigners warned that the UK was still not prepared to regulate online campaigning during the next general election, despite lengthy investigations into the use of Facebook advertising during the 2016 EU referendum.

All political parties expect the social network to be a major battleground during the next general election, with one senior No 10 source saying “this will be Carole’s worst nightmare” – a reference to the Observer journalist Carole Cadwalladr, who has worked to expose the Cambridge Analytica scandal.

Major parties are expected to dedicate a substantial proportion of their election spending to advertising on Facebook and its sister service Instagram. Individuals involved in those preparations said they expected the focus to be on using the social network, which on Monday announced a new range of transparency tools for political advertising, as a cost-effective broadcast advertising medium to promote simple messages to voters.

Sources suggested there would be less focus on microtargeting of small groups of individuals, not least because restrictions introduced since the last election on incorporating third party data from the likes of Experian has made this much harder. Instead, campaigns expect to use Facebook’s in-house targeting tools to automatically find audiences which are more receptive to their messages.

Topham and Guerin, who cut their teeth in Auckland politics, spent several years working as consultants for longtime Tory strategist Crosby’s CTF Partners lobbying company but are now focused on their own business.

The duo are reunited with Isaac Levido, another former protege of Crosby, who worked on the successful Australian campaign and is now in charge of preparations for the Conservatives’ general election campaign.

Allies and opponents privately describe Levido as a ruthlessly focused and effective campaigner. However, questions remain over whether he worked with CTF Partners when the business was supporting the party of former Malaysian prime minister Najib Razak, who was subsequently charged in relation to his alleged role in the 1MDB corruption scandal. Razak denies the claims.

Levido declined to comment when contacted by the Guardian as to whether he worked on the Malaysian contract but did clarify that he had never worked with Cambridge Analytica.

In a separate development, Crosby’s CTF Partners is being investigated for a potential breach of rules by the lobbying regulator relating to staff who did voluntary work for prime minister Boris Johnson’s leadership campaign – claims they strongly deny.

Crosby is a long-term ally of Johnson but is reported to have become increasingly detached from day-to-day operations during a power struggle with senior Downing Street adviser Dominic Cummings. As a result, he is unlikely to take part in the next election campaign.