How do I quit Safari when the Quit Safari is greyed out?

You may have an open dialog box and/or it could be underneath another application window. Since this may or may not be a scam dialog, you should force quit Safari — option+command+esc keys.

When you relaunch Safari, press and hold the shift key as you are doing so. This prevents junk from reloading. On the application menu, choose Clear History… : All History : Clear History button. If you have a Developer menu available, press option+command+E to clear your browser cache.

If no Developer menu is present, System Preferences : Advanced : √ Show Develop menu in menu bar. Then press option+command+E to clear the cache. The Developer menu must be present before you can clear the cache.

Many thanks. Will give this a go in the morning!!