Mathew Newton wrote:

I want to remove a UPVC window and having hacked off one side of
plaster on the inside I was expecting to find cleats similar to these
securing the window to the internal wall leaf:
Normally just frame fixings straight through the, erm frame, into the
masonry, can you see evidence of them on any openers?

The vertical plastic piece (held in with two nails and a bit of
plasterboard adhesive overspill) looks to me like it it some sort of
cavity closer
Exactly that.

Any ideas how this window is secured in place? Incidentally, the
inside of the frame shows no obvious fixings passing through to
anything either.
I'd expect to see them there, you do hear of some of them being
installed with foam only ...