I'm not sure what the regs are in GB but I would have concern with:
Microwave Ovens: Possible for any leakage to interfere with systems like DME, GPS, Rad Alt, and weather radar. I just don't know how "clean" the signal produced by one is. That being said, I have seen a few home type microwaves in US general aviation A/C. If your regs allow it I would advise a test flight to make sure it wont interfere with the avionics.
Coffee Pot: Home type coffee pots heat the water to 91-96 C So the odds are it will boil the water at inflight cabin altitudes, making bad coffee.
Also, if you ever dumped the cabin pressure at altitude, the coffee in the pot will most likely flash-boil and if the pot is glass it might shatter.