** Shares of Marston's MARS.L up 10% at 42.7p
** Stock is top gainer on FTSE small cap index .FTSC, which is up 0.05%
** Co expects annual PBT above expectations, as revenue management and operational efficiency initiatives lift margins
** Analysts, on average, expect co to report underlying PBT of 67.2 million pounds ($90.01 million), according to a company-compiled consensus
** YTD, MARS down nearly 3%, .FTSC up about 7% YTD
($1 = 0.7466 pounds)
(Reporting by Nithyashree R B in Bengaluru)
((NithyashreeRB@thomsonreuters.com))