I rinse out the milk bottles at the end of the wash and while still warm wring them out by twisting the ends. They rapidly cool and stay very compact without need to replace the cap.
Oddly different suppliers round here use two different plastics for the caps - one acceptable and the other not. They also manage to emboss the plactic type in 0.5 point font and I don't have an electron microscope to hand.
With the push to recycle and with local authorities taking only certain types, why is it not mandatory to show the symbol on all plastics and preferably in a size that most people can easily see. Lidl are quite good (are German rules tighter?) and Tesco are particulary bad at marking packaging.
If we could get consistent acceptance of plastics across authorities, then it should be an offence/attract a tax to sell products in plastic that is not acceptable for recycling. We could also put refundable 5p on ALL drinks containers, so the kids would not only leave less litter, but clean up other peoples (or doesn't 5p mean anything these days?)