UK's Big Yellow bottoms midcaps after Blackstone takeover talks collapse
** British self-storage company Big Yellow Group BYG.L falls 4.5% to 1,026p; top pct loser on FTSE mid-cap index .FTMC ** Co says no basis for continuing discussions with Blackstone BX.N on potential deal, after being informed of valuation level at which Blackstone could make proposal ** But did not disclose details of Blackstone's offer ** As of last close, BYG up 11.5% this year, FTMC gains 7% (Reporting by DhanushVignesh Babu in Bengaluru) ((DhanushVignesh.Babu@thomsonreuters.com))