For about 130 years from 1750 Mitcham, Surrey (now in the London borough of Merton), was an important herb-growing area, and among the herbs mentioned by Benjamin Slater, writing in 1911, was saffron, which was ‘like the shrub, cedar of Lebanon [Cedrus libani], growing about a foot high’ and ‘not grown vey extensively, being rather a dangerous plant’ [1]. Clearly this plant was not the usual saffron (Crocus sativus).
In the Pitt Rivers Museum, Oxford, is an item, presented in 1914, and used to prevent conception:
When a woman noticed that she has missed a period she puts about the same quantity of saffron as this envelope contains into a pint jug; pours half a pint of boiling water on to it, covers jug’s mouth with muslin and puts a saucer on the top. She leaves the saffron to soak and when cold, strains it through the muslin and drinks a wineglass-full for four consecutive mornings. She puts one sprig of saffron into each boot and wears it there for nine days. The idea of this being that as the feet get hot the saffron soaks through the stocking into the foot. The sprigs here contained have been so worn in the boots [of an Oxford woman].
Here again ‘sprigs’ of saffron doesn’t sound right, and on examination the sample proved to be of juniper (Juniperus ), rather than true saffron.
There a many records of juniper being used to produce abortion, and Geoffrey Grigson records bastard-killer as a Somerset name for the tree [2]. Similarly in a ballad about four ladies-in-waiting in the court of Mary Queen of Scots (1542-87), one of whom became pregnant and resorted juniper – savin – as an abortifacient:
She’s gane to the garden gay, To pu’ of the savin tree; But for a’ that she could say or do, The babie it would not die [3].
Strictly speaking savin is Juniperus sabina, a low growing species native to central and southern Europe and occasionally cultivated in the British Isles. If its twigs are continually cut back and harvested, it could easily look like the Mitcham plant mentioned by Slater.
Thus is appears that the name savin was corrupted to saffron, and applied to juniper.

1. P. Harris, The Mitcham physic gardens, [SLBI] Gazette, July 2003: 8-15.
2. G. Grigson, The Englishman’s Flora, 1987: 24.
3. F.J. Child, The English and Scottish Popular Ballads, vol. 3, 1889: 387.

See also discussion in G. Hatfield, Country Remedies, 1994: 17-9.

Image of juniper (Juniperus communis): Wiki Commons.