As I am never likely to be working / earning enough to repay the old style student loan (1995), is there a point at which the student loans company will give up asking for it?
None that's been declared in any legislation (yet). And its locked into your working habits via your NI number of course. The size of the loan increases in line with inflation as well.
The loan or remaining balance is written off after 25 years if you have been earning too little to have to paid it off by then.
This is the current rule - I suspect it doesn't apply to older loans. ISTR reading that they would give up asking about it when you reach retirement age, but haven't been able to confirm this.