Thanks for linking that thread and pointing out those sections with the links!
On a tangent, I’ve always found it interesting that Research Machines wasn’t in the contest, since it would have been such a natural candidate. There’s also an answer to this in that thread, quoted from one of those great The Register articles (thankfully provided by some BigEd),
Fischer realised that a machine based on the BBC’s hardware and software specifications and intended to be sold at the price the Corporation wanted could not be produced reliably within the launch timescale the broadcaster was set upon. RM chose not to pursue the BBC contract as it stood. It told the BBC it could produce the machine the Corporation wanted, but it would take twice as long to bring to market and cost twice as much.
Fischer was unsurprised, then, when Acorn’s BBC Micro was launched late, took far longer than planned to reach everyone who’d ordered one, and ended up costing more than forecast.
Which raises another question, namely, why was the BBC on such a short schedule? Was it, because everything seemed to be set with NewBrain already, or was it just some kind of ambitious “oversight” in the first place, which first looked like it could be remedied by simply adopting the NewBrain?
Edit: I get it that it was essential for this initiative to react quickly to social trends and technical development, but the plan was really ambitious. Rescheduling the program from Autumn 1981 to Spring 1982, when the NewBrain failed, was also really ambitious for any new computer to be developed, tested, rolled out to production, and eventually arriving in the shops.