I'm a member of WWT and visit The London Wetlands Centre often. It is well worth a visit. I see from your weblog that you are like to photograph wetlands wildfowl. The Barnes centre has plenty of options to photograph ducks, geese, swans etc. without the need for very long lenses. They do, of course, also provide plenty of hides and they are all close to the water so you can often get decent pics with medium telephotos.