** Shares of British private hospital group Spire Healthcare SPI.L up 5.3% at 219p
** Stock among top gainers in FTSE mid-250 index .FTMC which is up 4.98% YTD
** Leading investors of SPI, including activist investment trust Achilles AIC.L, are urging co to put itself up for sale, Sky News reported
** Harwood Capital Management entities, of which Achilles is a part, were among investors who believed firm was significantly undervalued, the report says
** Harwood Capital and Spire did not immediately respond to Reuters request for comment
** Including session's losses, stock down ~1.12% YTD
(Reporting by Ankita Bora in Bengaluru)
((Ankita.Bora@thomsonreuters.com))