Prompted by Martyn Brabbins mentioning it, http://www.colinscolumn.com/martyn-brabbins-remembers-harrison-birtwistle/, I returned to Theseus Game with curiosity and, having listened, much reward.

Ensemble Modern conducted by Martyn Brabbins and Pierre-André Valade. Given the lack of information on the YouTube posting I assume this is DG’s recording (coupled on CD with Boulez conducting HB’s Earth Dances).

https://www.boosey.com/cr/music/Harrison-Birtwistle-Theseus-Game/1511