Production of the 2500 M did not start until April 1972, six months after its presentation at Earls Court. As suggested, the 2500 M was powered by the desmogged (US specification) Triumph 2,498 cc straight six from the TR6. The engine developed 106 bhp at 4,900 rpm and was mated to a Triumph four speed gear box. The power was put to the rear wheels through a Triumph differential. In a Road & Track test, the 2500 M sprinted from rest to 62mph in 9.3 seconds and attained a top speed of 104mph. Rather modest performance figures that could entirely be blamed on the emission strangled Triumph engine.

It was clear that the M-series had much more potential. Right from the start the 2500 M was primarily manufactured for the American market. It was also available in Britain, but there it was overshadowed by the faster and only little more expensive 3000 M. As a result the 2500 M was withdrawn from the UK market in 1973. Production came to a premature end in 1977 when supply of the TR6 engines had completely dried up. Still the 2500 M would become the most successful M-series car with a total production number of 946 units built between 1972 and 1977.