The move follows successful trials on semi-skimmed milk products in more than 400 Co-op stores in August of this year.
The retailer will implement the changeover by the end of next month, it said, adding that switching green caps to clear will unlock a myriad of recyclability benefits.
Adam Williams, milk buyer at Co-op, said, "There are changes in store for how shoppers see milk bottle tops, with the new caps able more easily recycled and retained in the food sector, unlike their coloured counterparts. There is limited availability of food-grade recycled plastic, and that is a challenge.
"It is important that packaging is viewed as a valuable resource. We continue to work to explore new ways to make it easier to recycle and re-use these materials, it is a small change to an everyday issue that will collectively add up to make a big difference – a ‘clear’ solution that can reduce the dependency on virgin plastic in the supply chain."
By early 2023, the group will have removed red (skimmed milk) and blue (whole milk) caps from its own-brand range.
The move will cut more than 150 tonnes of coloured plastic from HDPE streams per annum.
Clear caps reduce colour contamination in the high-density polyethylene (HDPE) stream, allowing materials to be recycled more easily into food-grade packaging, Co-op noted.
Adam Herriott, sector specialist, resource management, at WRAP, said, “WRAP fully supports the complete removal of pigments from HDPE milk bottle caps by Co-op, a founding member of The UK Plastics Pact.
"This development has helped the HDPE milk bottle increase its reputation as a shining light of the circular economy and will enable the caps to be recycled with the bottle and go back into food-grade applications and therefore able to be recycled multiple times into high-grade, high-value materials and products."