** Bank Barclays' shares up 5.7 pct, top of theFTSE, after saying core pretax profit for H1 up 19 pctto 3.97 bln stg
** "BARC has produced a 6% PBT beat in its core business (excorp centre) in Q2," Jefferies analysts say
** Stock down more than a fifth since pre-Brexit toThursday's close
** BARC second-largest gainers on the Stoxx 600 Banks Index ; sector is up 2.3 pct and best performing in Europe
** A quarter of co's 30-day avg vols gone through by 0815GMT (venkateshasoumithri.mamidipudi.thomsonreuters.com@reuters.net)