Can't tell you his reason for vegan worcetshire sauce, but I can tell you mine. Fish. Deathly allergic. And anchovie paste is a main ingredient of the original sauce. Even small amounts causes my tongue to go numb, it's why I never eat a meatloaf made by someone else. You just never know what their family's secret recipe might contain, might be something like Lea and Perrins worcetshire sauce.
The vegan worcestershire sauce that was suggested for this Irish Stew sounds delicious. But, help me here...what is the point of using a vegan worcestershire sauce with a meat-based stew?