The share of British goods as a proportion of our total imports declined from 23% in 2015 to just above 7% last year, according to a detailed analysis of trade between the islands carried out by the ESRI and the Department of Finance.
The decline was offset somewhat by an increase in imports from Northern Ireland, the report concludes.
The proportion of incoming goods from north of the border increased from 1.5% to 5% in the aftermath of Brexit.
The report details an overall sharp decline in trade between Ireland and Great Britain since the UK's formal departure from the EU at the beginning of this year.
The effect on exports has been less dramatic, but nonetheless evident, with the share of Irish goods destined for Great Britain declining from just below 11% to 6.3%.
"The overall asymmetric impact is due to the more gradual introduction of customs procedures on inward goods in Britain with further delays on the implementation of these checks announced in the last week," the report concludes.
Some industries have fared worse than others with the food and beverage sectors particularly negatively impacted on the export side.
The greatest impact when it comes to imports is also seen in the food and beverage sector.
The Northern Ireland protocol is likely contributing to the boost in trade with Northern Ireland.
The protocol was designed to prevent checks along the border between Northern Ireland and the Republic, following Brexit.
However, it has been a source of tension between between the UK and EU because of the disruptive effect it has had on trade between Great Britain and Northern Ireland.
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Combined Covid and Brexit hit
As well as Brexit, the ending of the transition period coincided with the Covid-19 pandemic, which has also impacted trade flows.
"Although many supply chain challenges have come together since the onset of the pandemic, the greatest driver of the reduction in Irish imports from Britain can be traced to a Brexit effect," Martina Lawless, ESRI Research Professor and report co-author, explained.
"There has been a less substantial impact on exporters so far and continued good news coming from the deferral of customs checks on goods moving from Ireland to Great Britain which had been due to be introduced in January," she added.
The report bases its findings on an analysis of detailed trade statistics between Ireland and Northern Ireland and between Ireland and Great Britain.
"However, as data is not currently available on trade flows between Northern Ireland and Great Britain, the extent to which the increases in trade between Northern Ireland and Ireland are a result of substitution away from trade with Great Britain by Northern Ireland firms cannot be estimated at this point," the report authors conclude.
Professor Lawless told Morning Ireland that the impact of Brexit is most heavily felt by the food and drinks sector as new checks for compliance and sanitary checks impact this sector more keenly.
She said the ESRI compared trade flows north and east (with the UK) with the trade Ireland has with other individual EU countries and found that the "Brexit-effect" has been greater than the impact of Covid on trade with other countries.
She said that the changes in import patterns look set to remain, while exports remain at risk of rising costs and checks as Great Britain gradually increases the number of new regulations.