Although they are not supposed to pass through meters it would appear some of my neighbours may have homeplugs wireless or not to which these unknown devices are connected and therefore appear on our modem as "Currently connected devices". If that makes any sense.
If there is an unencrypted wireless connection available they do not necessarily need to pass through a meter
Can you tell from interrogating your broadband useage if someone is piggybacking on your connection when your own devices are not using data?
The complaint that you are experiencing slow results indicates that others may be using your connection as may be possible with any unencrypted system