Cod are one of the main targets of Winter anglers around the coast of the UK.
As a cold weather species to target you can expect to catch more Cod during the Winter when fishing from the shore. However they do tend to show from later August / September along the east Coast and the English Channel. The catches of Cod in the Mersey basin become noticable at the end of September.
The UK shore caught record stands at 44lb 8oz (Tom’s Point, Barry). The UK boat record is considerably higher at 58lb 6oz (Whitby).
If fishing from boats they can be caught year round in deeper waters. That said I have caught a 2lb Codling in the middle of Summer from a rock mark on Anglesey. If you can access deeper waters you may find them in Summer, they are sometimes darker in colour and refered to as Kelp Cod.
As a species they are opportunistic feeders and will scavenge while hunting. When targeting Cod in Winter good sized baits that will emit a strong scent trail work well.
Cod tend to move offshore and further north again during early March. Though a small amount will still be around longer.