I have the original sash window in the kitchen so the bottom half opens
for cleaning and the top half slides down for cleaning but does not
rotate inwards.

Technically to comply with modern standards, you'll need to replace the
latch with something less than 1.7m high or have some remote method of
opening (i.e. Mighton powersash). However, whether or not you need to comply
with modern standards is another issue. Fixing it to comply is serious
overkill.

In any case, just submit the building application to move the doors. You can
fit the kitchen after the door work has been signed off.

Christian.