Difference between Have a drop too much and Have a glass too much

have a drop too much —(coll. understatement) be rather drunk (also: take a drop too much):

• One night I had a drop too much and there was a bit of a row.

have a glass too much —(coll.) be drunk:

• The policeman said that Peter had a glass too much. Of course, what he had really had was a pair of glasses too little.