Older Brompton front brake cable I needed to replace the front brake cable on my old brompton, so (after a bit of searching) ordered what I thought was the right cable (QBRCABFA-M[3] from sjs cycles). Turns out, it was the wrong one and the nipple is too small for my brake lever.

As described in this blog post:
http://blog.brilliantbikes.co.uk/2015/05/brompton-10-degree-brake-lever.html
... brompton move away from their own brake cables to a more standard type in 2012.

It seems the old cables are quite difficult to find now, the front cable I purchased was the only one I could find that looked right. One option might be to buy this cable for the rear brake, and cut the cable to the right length for the front...

So, my question is, how can I get round this without buying new brake levers? Anyone have any other bright ideas?

(Pic below shows my brake lever)
Your own posted link says


  Brompton with the 10 degree brake levers with an open clevis should be
  replaced with either the 30 degree or new aluminium brake levers.


Sounds like the 10 degree ones risk the cable's mushroom falling out of the open clevis, rendering the brake inoperable.  That would be bad.

You should replace the levers with safer ones.