I think that david White's frame is the product of the original teaming up of Arthur and the former ace roadman ( as of course was Arthur) Wes Mason.
This must have been early on in the 1970s, before the duo teamed up with Ron Kitching who owned the Chapel Buildings that eventually became the MKM workshops. Incidentally the Chapel Building was demolished a couple of years ago to make way for a block of flats. It was a great pity, and there goes another relic of cycling's history. The building would have converted easily into apartments, but demolition yielded more flats.
Of the two Wes was the metalworker and, as the story goes Arthur was the businessman..that is when he wasn't riding his bike. I have read that Wes had worked as a framebuilder for Carlton, the company for which he rode as a Pro, but I am uncertain about the accuracy of this statement. Wes was a very skilled "fitter and toolmaker", a trade he picked up later in life when he closed his own Harrogate shop.
I recall meeting Wes when, in or around 1975/76 he joined a Further Education class to learn to braze "properly" By his account at the time MKM was in full production but Wes wasn't convinced that any member of staff had a proper training in welding and brazing/. At that time I was working as a Head of Department in FE, and had the pleasure of giving Wes his first two hours of instruction in brazing techniques. At that time MKM employed several local racing men such as the Macklams, both framebuilders, and Ian White, former T-T Record holder, as paint sprayer.
Even after the trio of M,K, and M split up in the later 70s, the firm continued to trade under that name..so it is pretty certain that the "MM2/"Arthur Metcalfe" is one of the very early frames that preceded MKM real. Wes is still around...last seen living in south Wales
And "Yes" MKM was a northern builder.
Norris Lockley, Settle, UK