I am probably wrong, but I would say that M would probably be compatible with the UK PAL system. I have noticed on some old cordless home TV distribution systems, a switch which changes the PAL system transmitter between two different pal systems. To my recollection it didn't make a lot of difference, possibly the sound was different slightly, could be mistaken there though. That was some years ago and auto sensing circuitry would cover that issue now in even the cheapest DVD player. Most incompatibilities these days are deliberately built in to make companies rich, not because they are genuinely incompatible. Like region codes!
The original reason that pal secam and ntsc exist is all down to when countries went colour and what technology was available, cos you couldn't keep asking your public to buy new compatibleTV's every time there was a breakthrough. Yet you wanted more reliable transmission systems. NTSC used to be known as Never The Same Colour twice by its PAL competitors.