I remember there was an unsupported claim RTD had to chastise Ncuti for also cursing too much.
It's not unsupported, Ncuti himself said it in his Radio Times interview.
“The only time I’ve ever gotten in trouble for anything was when I swore [while wearing] a Doctor Who costume. I got called into Russell’s office. Woo! And he let me know that that’s not acceptable. He said, ‘Do what you want when you’re out of costume, but when you’re in costume, do not let us catch you swearing.’ I was like, fair enough. And I guess that was a lesson. For the last four years I’ve been co-leading an X-rated show, and so I’m on a constant journey of learning what it is to be a PG role model and the lead of a family show.”
It makes sense, there have been plenty of clips of bystanders recording filming from around a corner or something, a viral clip of Doctor Who using what you might call violent sexual imagery or complaining about all the little SOBs is a serious risk.