There's a bloke at the bottom of the road who races sheds. Welds the doors up, bangs a cage in it, fuel cell, number flag on the roof and off he goes. He races on short ovals, although it looks like he may do a bit of figure 8 stuff as well.
Personally, I would far rather do a day of race tuition than a track day (even if I did have something worth tracking with!) - far better to learn how to do it properly than to drive round in an old banger and "thrash the arse out of it and scrap it".
If you do go for it, see if you can talk someone into trailing your Corsa there and back - many people have driven to track days and ended up with no transport to get them home, either as a result of the arse being thrashed out of it and it ending up as a steaming heap of scrap on wheels or as a result of enthusiasm being far in excess of talent and the car ending up as a steaming pile of scrap on fewer wheels than the designer intended...