We’ve a great tradition in Britain of making alcoholic drinks and liqueurs from the most unlikely hedgerow and garden ingredients. Often these were basically just adding flavouring to spirits.
In England at least, the cheapest spirit was gin. Gin was very variable in quality and flavour, hence many recipes use gin as the base spirit. I would suggest that today’s gin, being usually of good quality is not the perfect spirit and that a cheap vodka would be more appropriate.
These traditional sloe gin recipes come from my grandfather's wine recipes book. I've expanded and clarified them to make things easier for beginners.