M Steel, Dave Yates are from the same frame building workshop in Gosforth. MSteel had a reputation for building the Rolls Royces of touring bikes. Dave Yates was usually on MTBs, although the great man himself now lives in East Anglia and largely builds tourers these days.
It looks to me to be late 1980's. It will be a great all-rounder as it has mudguard eyes nad enough space for guards in the winter. A perfect machine for long days in the saddle. Ridden a century yet? It's the perfect machine for it.
You have a wonderful bike built with great attention to detail....enjoy. I'm jealous!
...and if you are ever selling...
Ride it or milk it!