What UK yarn can you use in stead of medium weight worsted weight and what needles should i use?

In the UK, you can use "double knit" (DK) yarn as a substitute for medium weight worsted weight yarn, although DK is slightly lighter. For this type of yarn, using 4mm to 5mm (US size 6 to 8) knitting needles is generally recommended, depending on your desired fabric density. Always check your gauge and adjust your needle size accordingly to achieve the best results for your project.