Late Beatles legend John Lennon's talent for songwriting was a result of profound heart-ache, according to bandmate Sir Paul McCartney.

McCartney admits he has often attempted to write emotionally charged lyrics for songs, but tracks always seem too "perky" or forced - while Lennon could do it effortlessly.

McCartney says, "John could write a great mean song. He had a lot of venom in him, whereas I had a pretty happy childhood... My dad didn't leave home, and my mum died of cancer rather than being knocked over like John's mum."