Basically depending on flow and depth, for bream you'll want some medium and large feeders from standard weight 30grams to 60 grams, (2 oz), unless there's a fair bit of extra water in.
A link feeder such as the Drennan comes into it's own on clear rivers when fishing for roach but quite often, particularly on rivers, you will need to add extra weight. If there's colour in and you're fishing for roach a groundbait feeder a couple of rod lengths out can be very effective and there is a good chance on the Avon of skimmers and bream on this line, however if it's not too fast and when practical I'd always fish past the middle.
The key is to ensure you hold the bottom and that the feeder is just heavy enough to hold.
The below picture shows typical Nisa and Drennan open end feeders in addition to a Drennan link feeder, noting that the open end feeders are available in weights from 3/4's of an ounce to 3 oz to allow for different conditions.
In flood water conditions the feeders in the bottom photo would come into play, noting these are chub and barbel feeders for big rivers such as the river Wye, Severn or Trent. Although it's unlikely you'll need feeders this size on the Avon I've added them for illustration purposes so that you can see where the additional lead has been added to allow you to hold the bottom in differing conditions.
