I think the Acorn Archimedes (1987) might be the closest UK vision to the Amiga. Of course it was 2 years later. But, mouse-oriented interface, graphics central, kind of 32 bit CPU with limitations (similar to the 68k which is 16 bit aspiring to be 32 bit), thoroughly weird desktop environment.
And a great BASIC with inline Assembly.
nitpick: ARM1/2 were 26-bit. The PC register used the bottom 26 bits for the address of the next instruction, and the upper 6 bits for status flags. Lots of code involves getting or twiddling those flags by amending the PC register directly. There is nowhere in the architecture you could put the missing 6 bits.
This was unlike the "24-bit" 68000 where the hardware package actually only had 24 address lines, but its address registers and PC were 32-bit.
https://en.wikipedia.org/wiki/26-bit_computing#Early_ARM_pro...
The ARM3 resolved the situation by adding a separate 32-bit clean PC register and a separate status register, instead of the combined monstrosity. All software had to be rewritten to use the new registers if it wanted to be "32-bit clean", unlike 68000 software which either just worked fine, or revealed the programmer was an imbecile who thought they could get away with storing random data in the top 8 bits of addresses.
Bonus: the Archimedes memory map (00000000-03FFFFFF, i.e. 26 bits) https://www.chiark.greenend.org.uk/~theom/riscos/docs/ArcMem...
In the case of Acorn they had hardware memory protection[1] and their own CPU designs[2].
In place of Irving Gould Acorn ended up with some clown called Stan Boland who decided it was better to change the name, stop making workstations and refocus on TV set top boxes. The company was dead six months later.
1. https://www.computinghistory.org.uk/det/29468/Acorn-MEMC-Dat...
2. Not sure whatever happened to the Acorn Risc Machine but I'm sure it'll turn up again. :P