I studied 'We Are The Lambeth Boys' at university a few years ago. It is an historic documentary and stands with 'Cathy Come Home' as a landmark piece of early British film. It was made to show what life was like for young (early adult) men and women in South London in the late 1950's.
It's easy to see why Moz would be drawn to film like this, depicting real young working class 'lads' in an time before political correctness hit Britain.
BTW. If you listen carefully, at around 2:51 mins in the song you'll hear someone say 'Oi, he looks queer doesn't he!'
Hope this is of some use.