Beanster.....
You piqued my curiosity so I went surfing. Here's what I found: The festival you mentioned occurred in 1970 - incidentally, the last performance given by Jimi Hendrix a few days before he died. Rory Gallagher performed "Sinner Boy" with his band Taste.
There's a video available: "Message To Love - The Isle of Wight Festival 1970: The Movie." Cost about $20.00 for DVD. I don't know if Rory is on there.
Thanks for the info.
Regards, Neil