"Steve" wrote in message ...

Never had one of those dual opening windows so these ideas may be shots in
the dark.
Could a childs safety lock that are fitted to kitchen cupboards be a basis
for an idea ( the kind when you open the doorway a little then depress them
to open fully )
If it was a 'normal' upvc window then I would say glue a little plastic
block in the track the hinge slides in or you could use a piece of soft
metal i.e. aluminium that had been sawn through a little so that it
restricted the opening in normal use but in an emergency the window could be
pushed out fully with a little force ( idea behind this were those glass
firedoor bolts) or you could fit a set of restrictor hinges from toolstation
etc
Talking of firedoors what about those cable tie type things they use on the
doors that break at a certain force but keeps the doors together if the
levers are operated by accident

Thanks a lot Steve, some useful thoughts there.

I visited a window supplier today in fact, and as I suspected, they
have a neat gizmo to attach to a normal window, but it would be fouled
by the tilt'n turn mechanism. I was mulling it over with the bloke
though, and he came up with the idea of a standard front-door security
chain, which sounds just the job. Now waiting to hear back from
BCO-lady to see if she will give it the seal of approval...!

David