Mini One 57plate loosing coollant

[Rogers gang]

can anyone help me please, my Mini One is loosing coollant but only when I am driving, I can leave for 7hrs while at work or over night and it doesn't loose any, this only happens while I am driving, I am having to top the bottle up every night. Does anyone have ideas what wrong.

[Rogers gang]

Hi, thanks all, we seam to be loosing it from the back of the engine, just seams to drip out when the engine is under pressure