Thanks to all the replies so far. It is definitely a microlight and has a 450Kg MTOW.
The aircraft is an S6 ESD XL. I visited her recently and noted that the last Weight and Balance was performed in 2002 which, according to the first link that Rod1 posted, would indicate that it the aircraft is overdue for another weigh-in. Is it a legal requirement to have a new w&b every 5 years? (it would appear so).