There was a feature on this on TV only a few days ago (BBC Watchdog, I think - check their site). Any powered means of transport is covered by legislation and requires insurance and possibly licensing if used on the public road or paths. However, you can use it on private land without any such legal implications - at will, free from the authorities' gaze, but you will need to operate safely and be aware of any third party liability (check with your home insurer)