Late Thin Lizzy rocker PHIL LYNOTT once "slipped" SIR Bob Geldof a line of heroin so he could bed his girlfriend behind his back.

The two Irishmen were partying in the late 1970s when Lynott tricked the Boomtown Rats frontman into snorting heroin.

Geldof recalls, "I'd never done it before and it was a f**king long line he gave me, which was very dangerous. But it was all deliberate on his part.

"As I had my head down the bog (toilet) throwing up, he sneaked into the bedroom and tried to jump into bed with my missus.

"I couldn't be angry with Philip because he was so sweet about it. He was just trying it on... To him it was just a laugh."