Yes. The BBC has a Motorola 6845 generating its screen addresses. That's a flexible chip, with which the developer has wide control over screen sizing and placement.
The Electron has a custom ULA designed by Acorn to produce the same video address generation as the 6845 when configured in one of the built-in modes but its functionality is fixed.
So on a BBC you can create, say, a 30-column display instead of the default 40-column display and the hardware will never even inspect memory beyond those 30 columns. On an Electron you can select between 40-column and 80-column output but those are your only options. If the programmer can afford only 30 columns of game graphics then at least 10 columns of game code will also be visible.
Minor exceptions are: using the mid-display interrupt to change the palette, and doing a similar thing with the tape output interrupt. So in both cases you don't change the actual width or height of the display, but you opt to make a vertical region of it blank by virtue of mapping all palette colours to black.
The former is usually used to reduce the 256-line output to the 156 bottom lines. See Spycat, Sim City or many others. The latter is much more rarely seen because it's not as obvious and because it severely impedes audio generation, the same counter being used for tape output and for audio generation, but contributed the small amount of empty space at the top of Southern Belle and Northern Star.