“This astounding elegy for 23 solo string players (10 violins, 5 violas, 5 celli, 3 double basses) was composed during the closing months of WW2 … his music mourns the loss of culture. Martyn Brabbins, Music Director of ENO, collaborated with LSO’s David Alberman to assemble a group of fellow musicians from all the London orchestras who, too, are mourning such a loss.” [Grange Park Opera website]

https://grangeparkopera.co.uk/whats-on/strauss-metamorphosen/

Filmed on June 7, posted by GPO on July 9, or yesterday the 11th (depends on what you read); also, although all the (professional) London orchestras are said to be represented, the GPO listing (below) does not include any member from the Royal Opera House Orchestra.

Violins

Igor Yuzefovich Leader BBC Symphony Orchestra
David Alberman Principal 2nd violin London Symphony Orchestra
Simon Blendis Leader London Mozart Players
Richard Blayden Sub-leader English National Opera
Annabelle Meare Principal 2nd violin Philharmonia Orchestra, and Vertavo quartet
Andrew Storey Principal 2nd violin Royal Philharmonic Orchestra
Charles Mutter Associate Leader BBC Concert Orchestra
Sophia Durrant Principal 2nd violin English National Opera
Miranda Fulleylove Leader UPROAR, Wales New Music Ensemble; Guest Principal London Sinfonietta
Sam Alberman [orchestra not stated on GPO site]

Violas

Rebecca Chambers Principal viola English National Opera
Duncan Anderson Co-principal viola English National Opera
Richard Waters Co-principal viola London Philharmonic Orchestra
Phil Hall BBC Symphony Orchestra
Bryony Gibson-Cornish No. 2 violaLondon Mozart Players; Marmen Quartet 

Celli

Tim Walden Principal cello Philharmonia
Tim Gill Principal cello London Sinfonietta
Dave Newby Co-Principal cello English National Opera
Joely Koos Co-Principal City of London Sinfonia and London Chamber Orchestra
Gillian Bragg Cello English National Opera

Basses

Graham Mitchell Principal double bass English National Opera
Joe Melvin London Symphony Orchestra
Gareth Sheppard Philharmonia