The singer-songwriter made the comments while being interviewed for a new two-part documentary on BBC Radio 2.
Of their first encounter, McCartney said: “I look back on it now like a fan, how lucky was I to meet this strange teddy boy off the bus, who played music like I did and we get together and boy, we complemented each other!”
Most of The Beatles’ best-loved songs are attributed to the songwriting partnership of Lennon-McCartney, although the pair famously enjoyed a fractious working relationship towards the end of their time in the band.
“There were a few songs that weren't very good,” said McCartney of their early output. “You know, [we were] clearly young songwriters who don't know how to do it.”
The artist then treated listeners to an example of an unrecorded Lennon-McCartney composition called “Just Fun”.
“Eventually, we started to write slightly better songs and then enjoyed the process of learning together so much that it really took off,” he said.
The two-part documentary hosted by his Lennon’s son Sean will commemorate what would have been the “Imagine” singer’s 80th birthday on 9 October.
John Lennon At 80 will broadcast on 3 and 4 October 2020 from 9-10pm on BBC Radio 2.