BSA Ultras and Scorpions are not regulated as standard, neither the early ones or the later "SE" models.
The regulator you have seen will be an aftermarket one maybe a "Tench" or a "HuMa" reg. There are other makes of regulator that have been made to fit these guns, basically similar in concept to the original Tench regulator (eg the HuMa) or direct copies of such regulators.
The SE models of both the Ultra and Scorpion have a pressure gauge fitted between the air tube and the firing valve, it is visible under the stock (hole drilled in the fore-end of the stock just in front of the trigger).
There are various aftermarket pressure gauges that fit on the filling end of the air tube that were fitted to the original models of Ultra and Scorpion, all retained the standard BSA fill probe method of filling the air tube.