That is the most ridiculous thing I've heard in a long time. Have you ever
seen a kitchen with space in front of the window? The sink is almost
invariably chosen to sit in front of it.

Having looked at Building Regulations Approved Document Part N3, you need to
ensure that the window controls are no higher than 1.7m from the floor if
you have kitchen units of standard height and depth in front of it.
Alternatively, you can install a remote operating system.

Part N4 indicates issues for cleaning the outside of the windows. Is this
the issue? If so, how high up is your flat? Does the window rotate round for
cleaning? Is there somewhere hard to place a ladder?

Christian.