I did this years ago and it was very simple: I had a certain amount of 'proper' instant coffee in a jar. Every time I spooned some out to make coffee I replaced it with an equal amount of decaf coffee, until the coffee in the jar eventually became all decaffeinated. Once I got to that change I was able to choose whether or not to have a (decaf) coffee, fruit tea, tea etc etc.. It took two or three weeks but I literally didn't notice the change. Good luck!
Estranged Son and Future Granddaughter
To think that London, or anywhere else for that matter, does not belong to any one demographic