This reminded me. I also found a Lego brick near the pre-decimal washing up liquid bottle and I brought it home and cleaned it up. The markings suggest it's also from the 1960s but despite being buried 60 years ago it still fits together perfectly with modern bricks and isn't showing more than a few scratches to show its age.My point was, theoretically isn't the plastics in biodegradable bags "better" than the stuff in Lego for instance...