▁Southern ▁Railway ▁later ▁built ▁the ▁surface ▁line ▁from ▁W im ble don ▁to ▁S utton , ▁via ▁South ▁M erton ▁and ▁St . ▁Hel ier . ▁The ▁t ube ▁extension ▁opened ▁in ▁ 1 9 2 6 , ▁with ▁seven ▁new ▁stations , ▁all ▁designed ▁by ▁Charles ▁Hold en ▁in ▁a ▁modern ▁style . ▁Origin ally , ▁Stanley ▁He aps ▁was ▁to ▁design ▁the ▁stations , ▁but ▁after ▁seeing ▁these ▁designs ▁Frank ▁Pick , ▁Ass istant ▁J oint ▁Manager ▁of ▁the ▁U ER L , ▁decided ▁Hold en ▁should ▁take ▁over ▁the ▁project . ▁▁ ▁With ▁the ▁exception ▁of ▁M orden ▁and ▁Cla ph am ▁South , ▁where ▁more ▁land ▁was ▁available , ▁the ▁new ▁stations ▁were ▁built ▁on ▁conf ined ▁corner ▁sites ▁at ▁main ▁road ▁j unction s ▁in ▁areas ▁that ▁had ▁been ▁already ▁developed . ▁Hold en ▁made ▁good ▁use ▁of ▁this ▁limited ▁space ▁and ▁designed ▁impress ive ▁buildings . ▁The ▁street - level ▁structures ▁are ▁of ▁white ▁Port land ▁stone ▁with ▁tall ▁double - height ▁ticket ▁h alls , ▁with ▁the ▁London ▁Under ground ▁round el ▁made ▁up ▁in ▁col oured ▁glass ▁pan els ▁in ▁large ▁gla zed ▁screens . ▁The ▁stone ▁columns ▁fr aming ▁the ▁glass ▁screens ▁are ▁sur mount ed ▁by ▁a ▁capital ▁formed ▁as ▁a ▁three - dimensional ▁version ▁of ▁the ▁round el . ▁The ▁large ▁exp ans es ▁of ▁glass ▁above ▁the ▁ent ran ces ▁ensure ▁that ▁the ▁ticket ▁h alls ▁are ▁bright ▁and , ▁lit ▁from ▁within ▁at ▁night , ▁wel coming . ▁The ▁first