Okay, another update.
I've just had a reply from Thomas Kirkham. Their standard tanks are fitted with dual pickups. By default, the lower pickup is connected and the upper pickup is blanked off, which can be used as a return feed if fuel injection is used. However, if the fuel pipe is connected to the blanked off connection and the free connection is then connected to an electric pump, you have a reserve fuel capacity at the throw of a switch.
Paul