More than a fifth of meat tested in Britain last year contained DNA from animals not listed on the label, according to the BBC.
The British Food Standards Agency (FSA) found 145 items out of 665 that it sampled in 2017 consisted partly or wholly of unspecified meat, it reported.
The products came from 487 businesses, including restaurants and supermarkets.
The FSA said the results, accessed under a BBC freedom of information request, were consistent with "deliberate inclusion", the broadcaster said.
But the agency added that the tests had deliberately targeted operations suspected of "compliance issues".
They were "not representative of the wider food industry", an FSA spokesman told the BBC.
Around half of the 145 contaminated samples came from retailers, which included three supermarkets, 50 belonged to restaurants and 22 originated from food manufacturers.
Some specimens showed DNA from as many as four different animals, while others contained no trace of the actual meat listed on the product label.
Supposed lamb items were most likely to contain traces of other animals' DNA, followed by beef and goat, while cow DNA was the most common contaminate.
Pig, chicken, sheep and turkey also featured frequently when not specified on packaging.
Mince meat was the product incorrectly labelled most often, followed by sausages, kebabs and restaurant curries.
The FSA was not available for immediate comment.
Its spokesman told the BBC that local authorities -- which had procured the samples for the agency -- were responsible for leading investigations and taking "appropriate action".
The European Union, which Britain is due to leave next March, toughened oversight of the food industry across the continent last year to prevent a repeat of a horsemeat scandal in 2013.
Millions of European consumers were shocked to learn then that a long list of supermarket items being passed off as beef or pork were in fact horsemeat.