"Gilbert v Hickinbottom" featured an exception to the general rule, where there were two properties in the same occupation, separated by a public highway. It was held that the functional connection between the two properties was so great that they were to be treated as a single hereditament. Functional connection is judged by the strength of the connection and the degree and nature of the separation. In "Edwards (VO) v. BP Refinery" name="E v BP">"Edwards (VO) v BP Refinery" [1974 RA 1</ref> the analogy of a spark plug was used to illustrate the principle.