You mention a British program. I do not know about the specific features you mention, but a British company called Serif used to make very highly-regarded DTP software.
Serif (makers of Affinity suite) were bought by Canva last year. So far, they’ve honored their perpetual licenses and still offer them, but it seems like a perilous proposition given Canva’s audience and sales model.
The last big RISC OS program written in BASIC and assembler. I published something through Cerilica called TextFX, also in BASIC and assembler.
There was also Composition, by a chap from New Zealand. Multiple transparent layers of any size and position, and and interesting system-wide plugin system.
I think they were bought by Corel
Edit: Serif are in the article, sorry