Hi Bryan,
MIRO - mass in running order - is the modern definition of the minimum weight of your van.
When you start loading stuff into it, like an awning, cooking and eating utensils, clothes, etc., the weight will obviously increase - and around 80 kg or more extra weight would be typical.
But I have a feeling that the old Astra 1600 8v had a towing limit of 1000 kg, so you would be illegal - even if you towed the Swift "empty".
To confirm this - look in the Astra owners handbook for the maximum towing weight for a braked trailer - it should be 1000 kg, but if you have a 2000 model year car that was registered in 99, it could be 1100 kg
And you need to re-confirm the MIRO for your Swift Challenger - my data says it now has a MIRO of 1240 kg - but this will be different for different years - so if you read the MIRO of 1016 kg from the data plate on the caravan then that's the correct value.
But as it stands, the answer is no.
Robert