What could be causing my car to squeal when turning left?

My Toyota Starlet has started making a squealing noise when I turn left. It squeals when the steering wheel turnes about an eigth of a turn and then stops if I go past about a quarter of a turn. It also stops when turning left when I brake. It seems to be coming from the offside rear wheel.

It's definitely not a loose belt.

Could it be the rear drum brakes? Does turning left put pressure on some part of the rear offside wheel which is defective or in need of lubrication?

Any suggestions would be gratefully received.