Sir Paul McCartney is still ''passionate'' about writing songs.

The 77-year-old Beatles legend enjoys working on new music just as much as he ever did and if his professional career was to come to an end, he'd still continue as a ''hobby''.

Speaking to Gary Barlow for a 'We Write The Songs' interview on the pop-up Radio 2 Beatles DAB station, he said: ''It's the passion. It's something you love to do. I always say if they stopped me now, I'd just do it as a hobby tomorrow, so it's just something you love to do.''

Paul previously teamed up with Kanye West on 'FourFiveSeconds' and 'Only One' and found working with the rapper a more ''cerebral''

experience than his partnership with the late John Lennon.

He said: ''I worked with him and it was a very interesting way of working. It wasn't two guitars like me and John used to be, this was more cerebral.

''It was just talking and thinking and me plonking away a little bit. And you record everything and he takes it away and kind of does stuff with itand just a month or so later, he sent ba ck this record and it was Rihanna singing and so I had to ring up and sort of say 'Am I on this? Did I have anything to do with it?' I couldn't tell!

''He said, 'Yeah, what it is is, that's you on guitar, so it's all the chords and the musical idea's yours, but we've sped it up to suit Rihanna's key, musical key, so I did it in A so now it was up in D'.

''You can imagine the fun of that. So when you're saying to me why do I do it, how do I do it, because it's all that kind of fun. And if someone like Kanye's going to ask me, then I'm going to show up.''

Despite their global fame, Paul and Kanye made a pact to keep their studio sessions secret if they weren't fruitful.

He admitted: ''What happened was I got word that Kanye wanted to work with me. So I just thought, 'Well, you know, I love his stuff so, here goes nothing.'

''So we did some secret sessions and we both said if it doesn't work out we just won't tell anyone!

Radio 2 Beatles is a four-day pop-up DAB radio station airing from September 26-29.