** Britain's Secure Trust Bank's shares STBS.L fall nearly 4% to 850p
** Co expects to raise its motor finance redress commission provision by about 16 mln pounds ($21.5 mln) to a total of 21 mln pounds
** Says the hike is to reduce its CET1 ratio by about 50 bps to 12.8%
** Adds provision could go up by 6 mln pounds more if FCA scheme implemented entirely
** The drop trims STBS's YTD surge to ~139%
($1 = 0.7450 pounds)
(Reporting by Nithyashree R B in Bengaluru)
((NithyashreeRB@thomsonreuters.com))