neil leslie wrote

Building Control say I should have
unobstructed access to the window for cleaning.

Building Control are wrong - if you have any problems with them ask them to
quote which Regulation they are applying. The Regulations are as follows:

Safe access for cleaning is covered by Regulation N4. The Regulation clearly
states it does NOT apply to dwellings.

Safe access for opening/closing is covered by Regulation N3. With a kitchen
unit or other obstruction not more than 900mm high below the window, the window
operating handle must be no higher than 1.7m above floor level. It can be 1.9m
if there is no obstruction.

HTH
Peter