From the label I'd say very late 60s to early 70s. I'm told St Michael started putting washing symbols on in 1968, so it's unlikely to be earlier than that. The phrase Made In Britain started to be phased out from 1970 (replaced by Made in UK) so it's unlikely to be much later than the early 70s either. Others may be able to comment further on the style. I see late 60s there myself.
