But the film is largely redeemed by an unexpected emotional resonance befitting a Steven Spielberg production.

Entering the tunnel, we pass a small shrine above our heads which contains a statue of St Barbara, the patron saint of tunnellers. It is traditional to have such shrines on every tunnel site.

In the following year blight appeared again, but at another point, and after cutting it out I put on tanglefoot, simply because I happened to have some with me when passing the tree.

Graphs can be prepared on blue-lined graph paper and then photographed or traced.