Martin Pentreath wrote:

Does anyone know of any extra-shallow microwaves which would fit in an
overhead cupboard or have any other ideas?

Ours - a standard full-sized one - sits on a shelf in a custom-made
larder unit; the gap is just big enough for the oven (subject to
adequate ventilation requirements), and it sits at the front of the
shelf, giving an almost 'built-in' look.

David