In order to make the game small enough to fit on a cassette tape they had to ditch basic and program the entire game, world in assembly.
Putting aside the fact that the majority of commercial games of the time were written in assembly (or other low-level languages) just as a matter of course, I strongly suspect that programming the game in assembly was an execution speed issue, and not a cassette space issue. Regular audio cassettes easily held enough data to fill an average 8-bit home computer's memory many times over, whether that data was machine code or BASIC instruction codes.
Found in an Edinburgh charity shop, so while it's not impossible, it's unlikely.
EDIT: Also, an NTSC signal on a plain PAL TV would be black and white (not even false colours) even if you got an otherwise stable picture.
It's easy to forget, but these old systems didn't connect to the TV with composite RCA connectors, but via RF. So we're not just dealing with straight PAL, but with PAL over a broadcast system. Scotland was using PAL-I for broadcast, while Poland seems to have used a combination of PAL-D and PAL-K. Differences in channel ranges and bandwidths, and sound channel offsets, could make it difficult to tune a TV set designed for one system to a signal from another, especially if it's a more modern set designed for automatic operation, as OP's set appears to be.