Hi Gibbo58
I'm actually not sure why I said that, but also try VikingOSX's suggestion:
"It is a complete scam. If in Safari, visit the Settings : Advanced panel and select Show features for web developers. That will add a Develop menu bar item. It also allows you to clear Safari cache and cookies via option+cmd+E.
Quit Safari, then holding the shift key, launch Safari again. Press option+cmd+E, and then from the Safari application menu, select Clear History… All History and click Clear History. Quit Safari. All history, cookies, and cache are empty.
Now launch Safari normally and don't visit the web site that popped that scam notice about viruses on your Mac."