Among advertising reviews there was a "lack of scale" with just seven clients with a media spend above £20m calling a pitch. This is compared with 11 in 2016.
Of the seven major businesses that called a review in 2017 just four went to the open market – Dreams, Hilary’s, KFC and Paddy Power.
Dixons Carphone moved to Abbott Mead Vickers BBDO without a pitch, and the Boots and Vodafone reviews were limited to WPP-owned agencies.
UK agencies were also kept busy with global reviews, including Airbnb, British Airways, Citroen, EA Sports, Ebay, Kia, Philadelphia and Lenor.
Overall the number of above-the-line reviews rose 9.2% in 2017 compared with 2016.
The number of media reviews may have been down – 22% year on year – in comparison to 2016 but there were several large companies active, including Barclays, BT, Carpetright Freeview, Ladbrokes Coral and Sainsbury’s.
UK shops were also heavily involved in major global media reviews such as Akzo Nobel, Carlsberg, P&G and PSA.
In the CRM sector, which showed growth of 9%, there were results for the BT/EE account, Costa and Ikea. The TV Licensing review that kicked off in 2017 is yet to come to a close so is not included in the figures.
The report explained that the types of digital briefs have changed as clients prefer to appoint "specialist agencies for digital strategy and innovation rather than communications". This sector had a 15.5% drop in the number of completed reviews in 2017.
Once again the retail sector had the highest number of reviews, followed by motoring, charities, alcoholic drinks and travel.
Kerry Glazer, chief executive of AAR, said: "Brand owners seemed to enter the year with a renewed confidence (or perhaps bravado) and the year started with a bang as reviews were called across all disciplines and sectors. Indeed, for many agencies, it was the busiest quarter in living memory in terms of pitching.
"It is always difficult to predict how the new business market will look in any new year, but as we enter 2018, we remain cautiously optimistic that volume levels will remain similar to 2017, although the size and type of review may well change.
"Equally, as agencies increase the number of disciplines that they can credibly deliver to their clients, it will be interesting to monitor whether this will lead to an increase in the number of major integrated reviews [which rose 8.4% year on year in 2017]."