Hello Dominik,
This site gives the answer I believe.
Photo sure looks like it was "U".
http://saafww2pilots.yolasite.com/bob-kershaw.php
Also Frost was shot down by ground fire on 15/03/41 in SAAF Hurricane "280" "W", ref "85 years of SAAF".
While Lt. RHC, Kershaw is noted as force landed on 20/11/41 with 1 Sqn SAAF.
Photo of "W", "280" on page 126 ofChris Shores " Dust Clouds in the Middle East".
AHotMEAW vol 1, page 319 has -
20/11/41
1SAAF Sqn
Hurricane II - Shot down by flak; 2Lt. H. P. Currin - POW.
Hurricane II - Damaged, force-landed at base; Lt. R.H.C.Kershaw safe.
It may also be helpful to find details of Currin's Hurricane ?
Alex