The high levels of the pollutant represent a dramatic increase on similar surveys carried out just six years ago.
Research also showed the presence of a species of shrimp not normally found this far north, which could be an indicator of climate change and warming seas.
The data was collected during summer 2022 by teams competing in the GB Row Challenge, a 2,000-mile event that circumnavigates Great Britain.
The aim of the research project was to build a picture of the many challenges facing British coastal waters. Using specialist equipment, the rowers gathered data on microplastics, temperature, noise pollution and biodiversity.
In 2017, Cefas (Centre for Environment, Fisheries & Aquaculture Science) published microplastic data from many of their offshore trawls.
It found just 0-1.5 microplastic particles per cubic metre (m3) that were bigger than 0.3mm in size. The samples collected during the Challenge event show much higher concentrations,...