My question is, other than using plugs and hooks, can anyone recommend a
method of attaching the plastic hooks to the uPVC windows which wont come
off and also, importantly, wont "damage" the uPVC frames? BTW the blinds are
between 1.2 and 2.6kg in weight

Depending on the layout of the windows, you might be able to get away
with an alternative method of hanging - we`ve almost given up on the
sticky hooks, but we`re a bit stuck for one window as its a bay where
the following won`t work...

You can get a "sprung" net rail from woolworths that you set slightly
wide and tighten down on a screw, then compress to get it into the frame
of the window - the spring keeps the rail pressed against the frame and
it generally seems a lot more secure than the hooks :-}

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