I have a UPVC window in my house, one of those ones where the top panel opens from the bottom and it opens towards the outside rather than inside. There's something wrong with the handle meaning it won't turn, which means the window can't be locked shut. Although it's only a small window, it's still a possible route for intruders to get in, so I want to find some way of securing it. Had someone come out to take a look at it, and apparently the locking mechanism is fucked and can't be repaired without getting a totally new window, which the landlord isn't prepared to pay for.

I was wondering if there were any security things I could buy and install myself to stop it being opened from the outside? I've looked at window restrictors but they seem to be more useful as a child safety mechanism than an anti-intruder mechanism.