Mr Honey picked up a nasty bruise on his knee on a recent visit to a country place. His memories of the episode are indistinct but he has offered that there was a fine cellar, that the place was all tangled up and Gothicked with ivy, and that really the people there should take more care.

I put it to him, rather as Holmes might have put it to Watson, that he had had rather more to drink than his hosts had expected, and had tripped on an ivy root as he took his leave.

Mr H had of course stumbled over the ivy question – debated in lively and well-informed fashion throughout the 18th century. On the one side Humphry Repton’s tutor Robert Marsham urged that it strangled trees and should be removed, while his critics remonstrated that it only colonised sick trees with thin canopies, and meanwhile provided warmth and valuable food for our finest song-birds. One sees the same division in the aesthetic school, with the poet Pope on the one hand admiring the clean pillar-like stems of his trees, and the astronomer and speculator Thomas Wright, wanting only to clad his with roses and honey-suckle.

William Marshall was an enthusiast, and on that account alone, I suspect that that amateur of excellence, Capability Brown, would also have recognised its value: ‘the usefulness of Ivy, then, in gardening, is to overrun caves, grottos, old ruins, &c. to which purpose this plant is excellently adapted; and were it not for its commonness, it would be reckoned inferior to few evergreens…’ Indeed Brown did use it to clad his ruins, at Roche Abbey, at Wimpole and elsewhere, but it is less likely that he would have planted it around trees and I suspect that, if only on grounds of tidiness, he would have objected to it in his clumps and plantations, though there might have been a place for it in the pleasure ground, where it could offer the associations of antiquity and of other-worldliness, as Lord Ongley found in his Swiss Garden at Old Warden.