** Shares of UK's Workspace Group WKP.L plunge as much as 16.6% to 312 pence
** Stock top percentage loser in FTSE 250 mid-cap index .FTMC, which is down 0.04%
** The British office-space provider says it expects a "substantial step down" in annual profit due to factors including higher operating expenses and falling rents
** Co also warns of a negative impact to valuation of its properties in the second half
** We expect a negative share price reaction to the trading statement as new CEO Charlie Green resets the business for future growth, Panmure Liberum analysts say in a note
** Including the session's losses, stock down about 22% so far this year, FTMC up 1.3%
(Reporting by Akshaya V in Bengaluru)
((akshayav@thomsonreuters.com))