Run by different companies, so bit of both (some had different stages with one studio building, though the ARC was one big interconnected multi-level set, but rarely if ever seen as such). Same catering bus for both, different breaks!I think you mean different STAGES in the same STUDIO lot.

One of the curious anomalies, similar to the Sulu thing in I Mudd, is that in "Light Duties" (Series 4, Episode 1) PC Ken Melvin places a bet in Reg Hollis's betting pool on Burnside becoming the new Detective Inspector, and a big deal is made about it, but by the time "Just Call Me Guvnor" (Series 4, Episode 6) rolls around, they make a big deal about PC Malcolm Haynes chasing Hollis about getting his payoff from correctly betting on Burnside. It's not impossible to reconcile, but it does stand out, as the former feels intended to be a setup for the latter, and both scripts were written by the same guy (The Bill creator Geoff McQueen), so I can only guess that actor unavailability played a part! 
