Larva on Broom

On a brief visit, yesterday afternoon, to a favourite site near Abernant, I took a close look at one of the three plants of common broom growing there and found lots of dark grey, almost black mines in the bark of the stems, plus abundant feeding damage to the green, fleshy wings that run along the bark. While looking at these, I noticed something tiny and yellow protruding from one of the stems, at the very top of one of the mines, which on closer inspection turned out to be a larva. I examined it with a hand lens and it seemed to be dead and damaged. I decided to leave it there and collect it on my way back to the car, but typically for me, I forgot all about it and went back by a different route.
This lunchtime, I went back for it and it was still there, in the same position, so I took it, along with the section of shoot it protruded from.
At home, I got it under the stereo microscope and  was amazed to see it was still alive, and swaying about very slightly and very, very slowly. I decided that either it was parasitised, had suffered some sort of mechanical injury or had somehow become trapped, so I carefully picked away the plant tissue surrounding it so I could inspect the whole of it and photograph it.

I can't decide whether it is Leucoptera spartifoliella or Trifurcula immundella, but based on the larval descriptions in Heath and Emmet, plus Dave's photos of the larva of L. spartifoliella on UK Moths, I am inclined to T. immundella and would welcome suggestions, please.