MediaSense, in association with ISBA and Ipsos Connect, conducted a series of in-depth interviews among 200 senior marketing and media decision makers.
It found that 58 per cent of marketers agreed that the number of agencies they work with would decline over the next five years. Meanwhile 54 per cent said they expect to bring a number of functions previously outsourced to agencies in-house by 2020.
These would be likely to include owned media, earned media, content management, data management and social media strategies.
While nine out of ten respondents were comfortable that media agencies will remain the go-to people for paid media, 73 per cent of marketers said they would increasingly contract directly with media owners and technology companies by 2020.
More than half (58 per cent) did not see media agencies as their first port-of-call for strategic advice on programmatic advertising, preferring to rely on their own resources or specialist tech or digital agencies.
Many marketers said they felt creative agencies were behind the curve, particularly in relation to the creation of dynamic content, such a social media.
However, eight out of ten said they still believe creative agencies would remain the best place to go for big creative ideas. Nearly 60 per cent anticipated that content development functions would move in-house or to alternative agencies within five years.
Graham Brown, the founder and director of MediaSense, said: "The ideal state is for organisations to be more self-reliant, data-driven and technology-enabled, with a clear view of the key drivers within their own media ecosystem.
"All marketing organisations should have a plan to ensure they have the optimal blend of capabilities (people, systems, processes and technologies) to enable them to succeed in 2020, irrespective of whether those resources are bought or rented."
The survey was conducted between March and July 2015.