The study, carried out by Ancestry, examined the genetic history of two million people via their home DNA kits.
Analysis of the test, which involves a simple saliva sample, traced ancestry back to over the past 500 years.
It found that the average UK resident is 36.94 per cent British, or Anglo-Saxon, 21.59 per cent Irish (Celtic) and 19.91 per cent Western European – the region covered today by France and Germany.
Scandinavia accounted for 9.20 per cent of the DNA, the Iberian Peninsula – Spain and Portugal – was 3.05 per cent and Italy and Greece accounted for 1.98 per.
Yorkshire was found to have the highest percentage of Anglo-Saxon ancestry (41.17 per cent), while the East Midlands has the most Scandinavian ancestry (10.37 per cent) as well as the most Eastern European (2.47 per cent).
There were marked differences between residents of England, Scotland, Wales, Northern Ireland.
The English had highest amount of Scandinavian (9.39 per cent) and French/German ancestry (20.45 per cent) and the least Irish ancestry.
Scots had the most DNA from Finland and Russia (1.31 per cent).
People living in Scotland have the highest amount of Finnish/Northwest Russian heritage (1.31 per cent), which is perhaps explained by their geographic proximity.
Within England, London is the most ethnically diverse region, having the highest amount of heritage from 17 of the 26 regions analysed.
Brits are only 37 per cent British
The East of England has the most Italian/Greek (2.53 per cent) and French/German ancestry (22.52 per cent), as well as the highest amount from the Iberian Peninsula (3.43 per cent).
Within England, the North East is home to people with the most Celtic ancestry (27.58 per cent).
Brad Argent, of AncestryDNA, said: “At a time when the concept of British identity is at the forefront of many people’s minds, it’s interesting to see that when it comes to our ancestry, we’re not as British or Irish as we may think.
“The UK has been a cultural and ethnic melting pot for not just generations, but centuries, and our DNA data provides a fascinating glimpse into our ancestors, including hints of immigration and emigration.
“While it’s fascinating looking at this data on a national scale, the fun really starts when you test your own DNA and begin to delve into your own family history.”