Summertime is best. Usually they arrive about August, and September is best. I use a fly rod on the beach to catch them in Dorset, but the normal is feathering off Chesil bank, Dorset, where they rake them in. Back in August, I witnessed am amazing spectacle- while reeling in a mackerel on a fly, two MASSIVE bass tried to catch it! They both swam around it trying to get in before the other. Eventually one got it, and stayed on the line for a few minutes before realising something wasn't right, and spat the fish out... And then it happened again a few minutes later. I've never seen anything like it, and that was off the rokcs on the shore. They won't be in the estuary though, you'll have to go out in the sea. I'm not sure if they travel that far north, but they might, it's worth a go.