John's neighbour operates an oil storage facility. John sees that the oil is leaking from his neighbours property and it is heading towards his property. In an attempt to prevent a loss from occurring, he decides to dig a large trench around his property which successfully contains the spillage and as a result no damage to his premises occurs. He submits a bill to his property insurers for the cost of constructing the trench, but they refuse to reimburse him, stating that the has been no damage to his property.

Advise John as to the extent of his insurer's liability, quoting relevant case law to support your answer.