In the original outline specification for the BBC Micro, there are several mentions of teletext, in particular
Graphics: […] (b) Plot a low resolution graphics point to build Teletext graphic characters in a range of colours or shades of grey (minimum: black and white) (PLOT X,Y,C probably C=-1 to complement point, C=0 to plot black point .... C=7 to plot white point)
Video display: […] The 'full screen' should consist of at least 24 lines of 40 characters (*preferably an option of 80 characters from the outset) of upper and lower case alpha-numerics and (colour) Teletext graphics.
and
Teletext: adapter should be available for off-air downloading of software
It seems to me these are two distinct and essentially unrelated requirements:
Display teletext characters on screen.
Be able to buy a peripheral that can download broadcast software.
The second requirement was presumably met by some special peripheral, that only a small percentage of customers would buy.
The first requirement was met by the SAA5050 teletext chip.
This chip added significantly to manufacturing cost, to the extent that the Electron omitted it. And according to an interview with Sophie Wilson
The SAA5050 was a pain - expensive and different from the rest of the machine
So it seems to me that it would be more efficient to meet the teletext character requirement just by including those characters in the software font for the bitmap modes.
Is there some other requirement implicitly included in 'teletext' that I am missing, that required the SAA5050?