potatoes

If you cut back the growth on them, then the tubers stop getting any bigger. This is normally only done if you get blight on main crops, to stop the disease getting into the tubers.

Lift a plant and check size of potatoes, if they are right for you then no harm done cut the haulms( another name ), Owlboggy is right they will just stop growing larger.

thank you qwdboggy and wyeboy your answers has been very useful