The success or failure of this tangy drink is partly reliant on the quality of marmalade used. For ease of use, choose "fine cut" or even "no peel"/"shredless"...
This is a wonderful drink however I would implore people to use as good quality marmalade as you can reasonably source. I made this with a blood orange and angostura bitters marmalade and that extra bitterness was just exquisite!