[DTV]

I may have gotten this wrong, but wasn’t the plan to keep the 1997 and use it along side BBC Reith? 

I know along side legibility, the other reason for designing their own font was reduced costs but surely as they own the copyright to the 1997 logo, they would no longer be paying to use Gill Sans as its now an image not not a font if that makes sense. I’ve been looking for an answer online but couldn’t find it.

Yes, the decision to replace the 1997 logo was taken incredibly late in the day - the original intention had been to simply gradually rollout Reith as a typeface department by department at the next natural rebrand (as per Sport in 2017 and News in 2019). Indeed, some of the original rollout materials even suggested that replacing the BBC logo was unnecessary and wouldn't be cost effective. You're also right in that the BBC did own the full copyright to the 1997 logo (which, as VMPhil points out, includes slightly redrawn letter forms anyway), so licensing was not an issue. I've always just assumed it was an impulse decision that sort of snowballed.