What studios? There is/was some recording activity for orchestral players in London, but not like (I believe) LA or NYC in their heyday. For that you need film or TV or pop music industries. Or advertising jingles. When the jingle industry flourished in Chicago in the '60s and '70s for some reason, lots of jazz players made good/great livings in that line of work because their talents and training gave them the ability to make the seat of the pants adjustments that such gigs often required. BTW, one of the reasons such situations arose so often in the jingle trade is that the guys from the ad agency who were in charge typically knew little or nothing about music and could only say something along the lines of "That's not what I'm thinking of/not what I had in mind" without being able to specify musically what they did want -- this while the guy who wrote the music (e.g., Marty Rubenstein or Dick Marx) tore his hair out. Then someone on the date like Art Hoyle or George Bean or Johnny Frigo or Kenny Soderblom would say, "How about this?" and play something that fit the ad guy's inchoate notion of what he wanted, and the problem would be solved. In a "time is money" setting, Hoyle, Bean, Frigo, Soderblom et al. earned every buck they made. I didn't think they ever played in public, only on recordings.