From Collins Pocket Reference : Whisky
John Murray & Co. have been producing Columba Cream for several years to a formula which is based on a traditional recipe. With five single malts included in its recipe, this high quality cream liqueur is an exceptionally fine example of its type. The company has offices on the Isle of Mull, and blending and bottling is currently carried out at their plant in Perth.
Tasting comment : A blend of five single malt whiskies, with the addition of honey and cream makes for a very plesant and mellow whisky cream liqueur.

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Source www.bbr.com :

Columba Cream Whisky Liqueur

Columba Cream is widely regarded as one of the finest cream liqueur brands on the market.

Columba uses a blend of Scotch single malt whisky, cream and honey to create an exceptionally smooth liqueur based on a centuries-old family recipe for brose.

Originally, brose was a traditional Scots family drink made daily using ingredients readily available- whisky, oatmeal, cream, sometimes honey, and sometimes fruit.