Thanks all for your help ...

... though some of the suggestions might not be suitable for a test drive!
My understanding is that you can't turn it off (though you can the traction control).
Why avoid it and at all costs? It is a personal preference thing (I'm not trying to tell anyone else what to do) but for me it would take away the whole point of buying one.
I'm no youngster and have had lots of small fun, light cars similar to the 100HP in character (AX, 205 GTI, 106 Rallye, etc.). That's my kind of car. I'm old enough that I could afford to buy and run a fast GTI if I wanted to but I don't. For me all the pleasure and satisfaction of driving comes from reponsiveness and feeling the car react to my inputs. That doesn't have to be at a silly speed, but it has to be reacting to me and not a computer.
Quite possibly it's slower on the road without ESP if you have to drive to a lower limit. But this isn't about speed, it is about the satisfaction of making the difference myself as the driver.
And also I do occasional small, fun, motorclub events like sprints in my current car. They have a 1400 class so a 100HP should be quite suitable. Any electronic intervention would make it pointless. It has to be my driving that makes the difference for better or worse.