I going to put back the old fluorescent... as I don't think I can afford a Class II as on the web the cheapest was £140 that I found.
I'm sure your old fitting is not class 2 so it needs to be earthed, and reinstalling it would be dangerous.Throw it away and get a class 2 fitting or a standard plastic ceiling rose and lampholder.
Earthing of lighting circuits has been a requirement since 1966, 55 years ago. An installation that age is way past its sell by date and should be replaced.
45 years I think you'll find.