Developed from a late 1880s design by Wolf Jahn, the Model "WJA", the "B.C.A." precision miller and jig driller inherited all the German Company's precision standards. In addition to the "WJA", Wolf Jahn was, of course, famous for their high-quality watchmakers' lathes and associated tooling. The concept of the machine - a swan-necked column carrying a slide-mounted head above a compound table topped with a rotary table - was then taken up by Leinen, another German maker of precision watch-making equipment. By the late 1920s, Leinen had developed the machine as their Model "80" or, with a plain compound table, as the "80a". Although these were smaller machines than later versions - the table was only 6-inches (150 mm) in diameter, the hole through the spindle 0.314-inch (8 mm) and the distance from column's inner face to spindle centre just 5 inches (130 mm). G.Boley also made a version of the machine, though this is a model far less frequently encountered than the Leinen BFL. Appearing to have a slightly heavier overall built, the G. Boley had much larger micrometer dials on the compound and rotary tables - while the latter had its "wheel" guarded by a neat sheet-steel cover, a feature lacking on the equivalent Leinen. By now, in the late 1930s, this lovely little jig-borer and precision co-ordinate drilling machine was in a form clearly recognisable as the immediate forbear of the later English-made Ultra, Excel and final B.C.A. versions.
With the outbreak of WW2, and supplies of German machines of course no longer available, the first British-made copy was almost certainly the version shown on this page branded as an "Ultra". At the same time, or very shortly afterwards, the  "Excel" version appeared (almost certainly by another manufacturer) and then, finally, the BCA.
The full story, with details of subsequent versions, can be found here