There are many claims to the origin of the parmo in Middlesbrough. An entry in wikipedia claims it was created in 1958 by Nicos Harris, a former US soldier who owned the American Grill on Linthorpe Rd.
In the 70s many places served them and they were often appeared on the menu as an Escalope Parmesan. Most also served an alternative, the Escalope Zagaroff. Greek places on Linthorpe Rd (the Rendezvous and the Heleneque to name two) did good ones and as mentioned above, they also served great steaks although I always ordered the T-bone over the porterhouse.
Stocktonites often claim that it must surely have come from there but there is really no history or tradition to back that up.