Shakes - Drayton is already the European indoor 400m champion .
Former 400m hurdles world record - holder Gunnell believes she can come back and compete over the barriers , insisting the Londoner is a ' potential gold medallist ' in the event .
Shakes - Drayton is already the European indoor 400m champion , but former 400m hurdles world record - holder Gunnell believes she can come back and compete over the barriers , insisting the Londoner is a ' potential gold medallist ' in the event .