It depends on what the "thick cream" actually is.
If the cream was made by taking milk (plain or cultured) and then mechanically churning it to a specific consistency - basically making dairy cream with more fat than your double cream - it will work. Any percentage cream or milk is mixable with any other, and you can calculate the resulting percentage in simple linear fashion. That is, if you mix equal parts 30% cream and 50% cream, the result will behave like 40% cream. The same will work if it was made by scooping up the butterfat risen to the top of cooked milk - which is the original, homemade meaning of "kaymak", but is almost never made, because of the huge expenditure of milk.
I am a bit skeptical about your product being exactly that though, so I will also mention other cases. First, if it is indeed made by churning, but the actual goal is butter, and it is simply not-yet-quite butter, it is questionable whether it will work, but I suspect that it won't. An elderly relative used to make homemade butter that way, and it was unlike commercial butter, but white, with higher water content, spreadable - and with a clearly crystalline structure, with the butterfat already coalesced. If you live in a place where this product is made but called "cream" instead of "butter", you can try it, but the chance of success is not all that high.
The second thing that could work is mascarpone. It is nominally a cheese, but in fact its texture combines with cream quite well, and the mixture can be whipped (I have tried it personally). Also, the taste is so bland that the result will taste like whipped cream, not salty or with cheesy notes.
There are a lot of other dairy-based spreads though, made in different ways, and pretty much none of them will work. Some are actually cheeses, like cream cheese (not only the American style, but also variations like Krema on the Balkans), ricotta, and others. There are also cultured dairy products (créme fraîche), reduced milks and creams like katmach and evaporated milk, and modern technological creations that use thickeners (frequently labelled just "spread" in the supermarket, but modern kaymak from the store is also made that way). If you don't know exactly how your spread is produced, it is more likely to be one of those, than to be churned-cream-halfway-to-butter.
So, if I were you, I would certainly do it if I knew it for sure to be a churned cream. Else, I would not expect it to work, but maybe make an experimental batch just to see what happens, fully prepared for it to not whip.
