[Inactive] £100 fine to view adult site!

When I visit a certain freely available and legal adult website, after a couple of minutes a message appears purporting to be from the police and with a reference to BT also. My webcam switches on and I see myself on a part of the screen. The message says that if I wish to continue to view that website I have to pay a 'fine' of £100 then access will be restored. I know it's a scam but the problem is that the message takes over my screen and I can find no way of deleting it or unsubscribing. the only way out is to restart my PC. Can anyone help or advise please?

 

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