Beef over the steak.
Asked what the meat was, staff at JD Wether spoon and Hungry Horse either did not know or said it was British beef.
But three out of nine meals sampled at Hungry Horse and four out of six at Wetherspoon had DNA from zebu - hump-backed cattle bred in the tropics.
Zebu is ruled poor quality by the English Beef and Lamb Executive.
Both chains defended their menu. Hungry Horse said it had served "millions of satisfied customers". Undercover Mum is on ITV1 at 8pm.