LONDON (Reuters) - The theft of money from accounts at Tesco bank is unprecedented in Britain and how it happened is still unknown, Britain's financial watchdog said on Tuesday.<div><a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=6_By73yzcjM:sPP0GudzSvY:yIl2AUoC8zA"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?d=yIl2AUoC8zA" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=6_By73yzcjM:sPP0GudzSvY:V_sGLiPBpWU"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=6_By73yzcjM:sPP0GudzSvY:V_sGLiPBpWU" border="0" /></a> <a href="http://feeds.reuters.com/~ff/reuters/technologyNews?a=6_By73yzcjM:sPP0GudzSvY:-BTjWOF_DHI"><img src="http://feeds.feedburner.com/~ff/reuters/technologyNews?i=6_By73yzcjM:sPP0GudzSvY:-BTjWOF_DHI" border="0" /></a></div><img src="http://feeds.feedburner.com/~r/reuters/technologyNews/~4/6_By73yzcjM" height="1" width="1" alt="" />